I'm not a holocaust denier or anything, it just seems odd.
There were a few reasons why survivors were kept alive by the Nazis rather than being killed outright, though those reasons varied depending on the time frame one is talking about, as well as who the survivors were in the custody of.
For the majority of the war, the most pressing reason why a large number of survivors were kept alive was their use as slave labor in the war industry and agriculture. This was done for a multitude of reasons, though the one key reason was that it allowed the Third Reich to free up able bodied men to enter the armed services. Also the Nazis would try keep a sharp eye out for skilled laborers in the occupied territories (as well as Germany) so that they could be utilized for Germany's war industry rather than being murdered outright or sent off to die in a labor camp. Though for obvious reasons, being a skilled tradesmen or craftworker wasn't a guarantee that one could avoid certain death or hardship while in Nazi captivity.
For example, the Mittelbau-Dora concentration camp (a sub camp of Buchenwald) supplied slave labor for the Mittelwerk factory. Mittelwerk was the main production facility for the V-1 and V-2 Rocket programs.
Now, towards the very end of the war, slave labor still played a large role in why many Holocaust survivors were kept alive by their captors. Though by the beginning of 1945, ulterior motives began to take root as the writing on the wall became clearer and clearer for German leadership, specifically the head of the SS, Heinrich Himmler.
Himmler (as well as Eichmann and other high ranking members of the SS) actually attempted to keep many Jews and other persecuted parties (specifically Jews and other persecuted parties from Western Europe) under his control alive towards the final stages of the war, but not out of some grand gesture of humanitarianism, but out of an attempt to use them as bargaining chips with the Allies in exchange for money and goods. Himmler made a number of gestures to the Allies, many of which were through a Swedish Red Cross representative, Folke Bernadotte (whom he also submitted a peace proposal directed at the Western Allies in April 1945 that would allow Germany to continue fighting against the Soviets), that he would be willing to ransom several thousand Jews in his custody. Himmler did this both as a way to gain money and material to continue the war effort, as well as to try gain favor with the Western Allies, whom he believed were indebted to the Jews, and as a result would allow him some form of power or leadership in Post-War Germany. This obviously did not work out the way Himmler had intended it to.
Another reason was that towards the very end of the war, command and communication began to breakdown to the point of not existing at all in some areas of the Third Reich. Many camp commanders were often given broad orders to evacuate their camps/facilities that were on the verge of being overrun and to proceed either to other camps or facilities to ensure they and their wards did not fall into Allied hands. This often resulted in brutal marches that lasted for days if not weeks in which hundreds of thousands of prisoners were marched around to the point that tens of thousands were killed either by the harsh nature of the march or by their captors during or at the end of their march. More often than not, many of these marches seemingly had no end point, and were seen as a final strike against the persecuted groups by the Nazis so that those groups would be unable to see the fall of the Nazi regime.
Sources: The End: The Defiance and Destruction of Hitler's Germany, 1944-1945 by Ian Kershaw
In the book The Great Escape, the Germans at Stalag Luft III moved a few people they thought to be major players in ongoing escape plans. They may have done this preemptively in these concentration camps to prevent escape committees or other inside groups from forming. This would only be applicable to moving a few at a time.
This may also be due to labor shortages in other camps where forced labor was exercised.
Just remember that concentration camps and extermination camps were vastly different.
Many concentration camps were a part of the slave-labor workforce. This comprised of 20% of Germany's workforce at its peak. Furthermore, someone able to work has value. Those no longer able to work would be among the first to be shot.
This is an excellent source detailing the difference between the two - http://www.holocaust-education.dk/lejre/koncudd.asp
This details death marches, and may help to better answer your inquiry - http://www.ushmm.org/wlc/en/article.php?ModuleId=10005162
It is important to point out that not all concentration camps created by the Germans had the same purpose. Recent research by the US Holocaust Memorial Museum has indicated that there were likely[ tens of thousands of camps scattered throughout Europe] (http://www.nytimes.com/2013/03/03/sunday-review/the-holocaust-just-got-more-shocking.html?pagewanted=all) as part of a vast and complex network.
Many camps were set up as waystations for prisoners being sent along to other sites, some were permanent work/slave labor facilities, while others can be considered extermination camps where nearly every prisoner was killed shortly after arrival. Some camps were hybrids (like Auschwitz-Birkenau) and served multiple roles.
Many victims of the Holocaust who entered the camp system were sent rather quickly to extermination camps as Sobibór. There were relatively few survivors of these locations with only 58 survivors following more than 170,000 killed at Sobibór. Because of this, most people who survived the Holocaust were "lucky" enough to have been sent to slave labor camps or hybrid camps. Based on economic need and eventually the German retreat from Eastern Europe in 1943-1945, many of these survivors were moved from camp to camp.
In other words, while many victims of the Holocaust were sent rather quickly and directly to their death, many survivors were sent from camp to camp before liberation.
I highly recommend reading Saul Friedlander's two book series on Nazi Germany and the Jews. It is accessible to casual historians but draws information from relatively recent scholarly work. Most of the material in this post comes from the second book entitled Nazi Germany and the Jews: The Years of Extermination.
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It may be convenient to simplify our understanding of the Holocaust by treating it as some monolithic, thought-out scheme with extermination as the purpose from start to finish, but that isn't truly the case. When we talk of the Holocaust, we are talking about a variety of activities and policies that were not necessarily uniform across all areas nor unchanged throughout the period of the Holocaust.
Even after extermination had displaced displacement, deportation, and slavery as "final solutions", the need for labor both in the war effort and in the apparatus of the camp system meant that at least some number of victims had to be kept alive at least for a while. On top of that, the actual effort of wholesale genocide was no simple task, and the Germans and their allies only had so many resources they could press into that purpose while they had a war on two fronts to fight.
I don't have any specific examples of transfers from one camp to another but it would make sense for this to happen as perhaps maybe slave labor was needed in one location while there were surplus prisoners in another, or if a makeshift camp were being emptied with the prisoners transferred to a more permanent camp, or, grimly, as death camps became established, other concentration camps without the machinery of extermination simply may have transferred prisoners to death camps to be killed.
Follow up question, did the movement of holocaust victims increase or decrease as the war progressed?
The relocations were mainly due to the changing borders of the Nazi reich. During expansion phase, new prisoners were made and new concentration camps were established in the east. When the allies pushed the front back in western direction, prisoners were relocated towards the centre of the Reich "to remove evidence from concentration camps and to prevent the repatriation of prisoners of war".
Historian Karin Orth names the following reasons for the Nazis to keep their prisoners alive; to abuse them as working slaves who should build an invincible fortress for the final fight, ... as hostages for negotiations with the allies, or as workforce for the expected anti-communist new start.
Karin Orth: Das System der nationalsozialistischen Konzentrationslager. Hamburg, 1999. ISBN 3-930908-52-2, p. 332.
This answer is used some reference to Judgment at Nuremberg, and some sources that you can find from various prominent Holocaust sites- let me know if this is sufficient for an answer! Without reference to a particular survivor, I can give an answer about the larger trend.
If it looks like the moving around of the undesirables is inefficient when the Nazis could have killed their victims on the spot, that is largely reflective of the fact that the Nazis did not have one plan for undesirables such as Jews at the outset of their seizure to power, or even at the outbreak of the war. While violence against Jews and their political enemies had taken place all throughout the 1930s, there was no formal plan to exterminate all undesirables at least until the early 1940s. The genesis of the infamous "Final Solution" is not entirely known as it likely has its roots in earlier Nazi ideology and practices such as the death squads operating in the USSR as the German army advanced. We do know that in 1941 "Operation Reinhard" was put into place which called for the extermination of all Jews within the "Generalgouvernement", an order coming straight from Himmler. From there a general extermination plan was rolled out haphazardly across eastern and central Europe, and became more systematic as the war progressed.
Before the 1941 Operation Reinhard, there were already nearly a dozen major camps that had been created as needed during the 1930s. Many of these camps were forced labor camps which utilized prisoners for the war effort. For example, Dachau had been in existence since 1933 as a forced labor camp. According to one site, 11 of 24 major Nazi concentration camps had been around before the start of Operation Reinhard. While many of these camps were deadly in their own right due to conditions and hard labor, the immense scale of the killing demanded by the Nazi extermination plans necessitated the opening up of new camps that could fill the requirements of massive killing. Some early camps were just not equipped for such programs, and as the Nazi leadership organized the logistics of the Holocaust, some prisoners were transferred to multiple camps.
With some exceptions, the Nazis were also careful about moving their prisoners far away from the areas where they lived before they killed them. Slovakia initially allowed the deportation of tens of thousands of Jews, but upon hearing reports of their fate, refused to allow further deportations.
Sources: Judgment at Nuremberg Jewish Virtual Library: http://www.jewishvirtuallibrary.org/jsource/Holocaust/major_camps.html United States Holocaust Memorial Museum: http://www.ushmm.org/wlc/en/article.php?ModuleId=10007328
fyi, you'll find more on this question in these threads
If I could ask a similar followup question: What exactly was the purpose of the extermination camps? How could it have been easier to gather up all their victims and then ship them somewhere to die efficiently, than it was to just kill them as they were gathered? Was it just to make disposal of the bodies easier and safer?
As many of the other comments mentioned, there were types of camps that served different purposes. One example is Terezin, which was a concentration camp near Prague. Unlike the death camps in the East, Terezin, as it's name suggests, a concentration camp, where people where held, particularly older Jews from Czechoslovakia. Well into 1944, it was used as a propaganda camp to show the world how the Reich was treating the Jews. There was even a movie made, put together mostly by prisoners in the camp. However, that is not to say that the conditions there humane for the rest of the time. Overcrowding was endemic, and thousands died of the effects of that, including hunger and disease. The fortress of Terezin, however, was not equipped for the sort of mass killing that Holocaust entailed, so thousands of those held there were sent to the death camps further east.
This documentary made using footage taken by the allies when they discovered the camps ( http://www.channel4.com/programmes/holocaust-night-will-fall/on-demand/57245-001 ) suggests they were moved to hide the scale of the atrocity from advancing troops.
Warning. Its the grimmest footage you will ever see. A must watch however. Anything you read does not put it into perspective.
Because Holohoax.