I haven't been playing guitar very long but this came up for me. I play a Takamine G series, nothing special but not a piece of junk. I noticed one time when I was playing that I was getting buzzing on certain frets on certain strings.
Obviously this would be caused by a warping of the neck of the guitar. Instead of messing with the truss(right word?) rod that goes through the neck, I asked about it at a music store. The guy there told me that the neck may have been warped from the way the guitar was being stored. He mentioned that a humifidier really helps in keeping the wood in good condition. Especially if you're playing an expensive guitar with nicer, more sensitive wood. It's just like wood in any other form, when it dries up too much it changes shape.
At the time I was living in a college dorm and it was ridiculously dry. Now whether or not that's actually what caused the buzzing on the guitar I have no way of telling, but it does make sense.
I fixed the problem by sliding a very thin slice of plastic under the bridge to raise the strings a hair and the buzzing stopped, didn't seem to change the action on the guitar either.
Anyway, that's what the humidifier is used for. I don't think I actually know anyone that uses one but i'm sure it wouldn't hurt especially with a higher end or vintage guitar. And if you notice in a lot of music stores they keep their acoustics in a seperate, climate controlled room for these same reasons.
Hope it clears it up.
so any information will be appreciated 
