I know from personal experience, +1 on the fact short bursts are easier on your gun than anything else.
Long bursts strain the motor and run higher risks of dry firing when you run out of ammo (one shot dry firing is like 10 shots firing BB's). Using semi auto only wears your motor, trigger block, trigger spring, and your trigger immensely. I go through about 800 rounds a scrim, about 350 of which are shot in semi. I've gone through 5 trigger springs and 4 triggers on my M4....
But if you've got a good piston (prometheus, system supercore, stock TM) and a good gunsmith, don't worry about the rest breaking down!