I always see press conferences there and headlines saying 'the President at Camp David', but are there any other lesser known reasons?
It's a presidential retreat built during the New Deal under the WPA. It was initially to be a camp for federal employees' families, but FDR turned it into a presidential retreat.
I think the reason it is still used is the diplomatic connotations of the name, along with the beautiful rustic Appalachian mountains. I would speculate that the environment can influence negotiations, in it's splendor & isolation. For important diplomatic negotiations, not every party may find the deal to be comfortable, but at least they will have a nice place to stay.
A somewhat amusing story: in 1959, Einsenhower invited Khrushchev to a summit at Camp David. The Soviet leader initially feared that the choice of this location was an insult:
"I was afraid that Camp David was ... the sort of place where people who were mistrusted would be kept in quarantine. ... Not even our Embassy in Washington could tell us for certain what Camp David was."
Source: Khrushchev's memoirs, as quoted in Nelson, The President is at Camp David.
Camp David was one of the first training facilities for the OSS (Office of Strategic Services) in the early years of WWII. One interesting 'secret' is the fact that Bill Donovan used the property to train American volunteers for missions in Europe where they would organize sabotage and espionage activities among leftist partisans. Many of these Americans were Communists who fought in the Spanish Civil War, so they were able to engage contacts they had developed during their time in the International Brigades.
Peter Carrol writes a bit about this in The Odyssey of the Abraham Lincoln Brigade: Americans in the Spanish Civil War
In "Thirteen Days in September," a book about the Camp David Peace Accords, Lawrence Wright claims Jimmy Carter wanted to sell Camp David as part of his efforts to diminish the grandeur of the "imperial presidency." He was dissuaded when aides told him about the network of nuclear bunkers beneath the complex designed to allow the President to run the country after a Soviet attack. Apparently there are elevators to the bunker complex in the cabins' closets.
