I've found it matters quite a bit when performance margins are close. I carry a rag in my bag for this exact reason. Using water out of my bottle I always have anyways usually does the trick and keeps the mechanics from yelling at me. Don't forget the tail rotor.
When I was taught to do it, twas at flight school in a salty environment with 22s. Seem to remember it could drop your MAP at a hover by an inch or more if I'm remembering correctly, but it's been a while.
Mike