The reason why Auschwitz-Birkenau was so large compared to other camps like Treblinka was that the Auschwitz-Birkenau complex had multiple, at times overlapping, functions. The evolution and the growth of Birkenau proceeded in a tangled trajectory, but one of its functions was as a source of slave labor by POWs or imprisoned Slavs. The use of the camps for labor was one of the reasons why the Auschwitz-Birkenau needed its complex of barracks and other facilities. The Reinhard death camps' primary focus was the extermination of mass numbers of people. They were not meant to be major sources of labor or serve other purposes that necessitated the keeping large numbers of inmates alive outside of a few Sonderkommando.

Auschwitz-Birkenau was a major extermination center in addition to being a labor camp. Its extermination facilities were also more advanced than the Reinhard camps and represented the internal competition within the SS for the best methods of killing racial undesirables. Franz Suchomel, a guard at Treblinka, outlined the differences between Treblinka and Auschwitz-Birkenau in his interview for the documentary Shoah:

Suchomel (S):Then stretchers were built. Say, can you translate that for him? Stretchers for carrying. Primitive stretchers were built...

Lanzmann (L): Primitive ones?

S: And then the corpses were put on them and carried to the trench.

L: Yes. What was the capacity of the new gas chamber?

S: The new gas chamber. Well, you could be done with 3,000 people in two hours.

L: Yes. Done. But how many people could fit into the gas chamber?

S: That – I can't tell you exactly as a German. The Jews say 200.

L: 200?

S: Yes. 200. You have to imagine that in one room that's the size of the room over there.

L: In Auschwitz, it was a lot more.

S: Yes, Auschwitz was a factory.

L: And Treblinka, that was a...?

S: I'll give you my definition. Remember it. Though Treblinka was very primitive, it was a well-functioning assembly line of death.

L: Assembly line?

S: .... of death. Do you understand?

L: Yes, yes, yes. I think you're right. Quite primitive.

S: Primitive. Granted, primitive. But a well-functioning assembly line of death.

As Suchomel's chilling interview notes, the Reinhard camps were more than capable of killing masses of people without possessing a major infrastructure. Auschwitz-Birkenau was a beneficiary of this process as it was in Suchomel's word, a factory. That meant the camp had multiple components in addition to mass murder.