In a lot of the brands of put together furniture, the fasteners are such that the fastening connection is between two pieces of hardware vs. hardware to wood. These are pretty safe to disassemble. Any time you have to screw directly into the wood, and remove the screws from the wood, I'd be very cautious about disassembling that part, particularly if it's weight bearing.
edit: I have a sauder desk that's been dis/re assembled at least 6 or 7 times. It won't go through a doorway otherwise. I bought it when a p100 was top of the line, however many years ago that was.