That depends on the time of year and if it is being heated or cooled.
Without A/C in a humid climate, there may very well be some mold on various surfaces and you may find that wooden furniture drawers are swollen and be harder to operate until the air is conditioned.
Some dust may accumulate as well.
Howsoever, if you leave the place clean, there will be little to do when you return. If the electricity is kept on, and it is summer or winter time, you can leave the heat on 50 degrees and the A/C on 78 degrees. You may also want to invest in some lamp timers to set lamps to go on and off, making it appear as though someone is home. If you will be away, do have a friend check on your place. Close off every water valve you can (washing machine, under sinks, dishwasher, water main into home), so if there is a leak somewhere, you minimize the damage. If you are not disconnecting the electricity and do not care to light lamps, then turn off the main electrical breaker. This will protect power surges if the power goes off and also save you money because anything that is plugged in is drawing a slight amount of electrical current and will cost you for no good reason.
I left my home (not apartment) for 7 years. Four of which it was climate controlled and three years everything was turned off. The only damage I incurred is that some minor mold attached itself to some woodwork/furniture. I was later told if I were to do that again, I should put a good coating of Liquid Gold furniture polish on my furniture to keep it looking good.