Why do passenger aircraft have the little airjets over each seat?
Why do airliners have them? Because passengers like them.  

When you're sitting in the penalty box waiting for a departure slot and the air conditioning system is barely running the extra cool air you can get from those vents may be the only thing keeping passengers from strangling the screaming child kicking the seat.

Also a common "cure" for airsickness is fresh air -- blowing cool air over someone's face will often help with symptoms of motion sickness, and may prevent a nauseous passenger from actually vomiting. Opening these overhead "gasper vents" and directing them at the passenger's face provides a quick way of doing this.