The ability to change tunings is one of the most convenient things about playing guitars. You really can't do that on any other instrument and have it sound as good. Most of the time, guitarists are tuning lower to fit the range of the singer (Van Halen, Alice in Chains, etc.) and to also get a heavier sound on the guitar in the case of severe "down tuning" (Slipknot, Korn, etc.) It can also be a combination of the two.
I play with a singer who writes a lot on the piano, so he tunes his guitar down to Eb to make the open chord shapes work along with the very "black key" dominated piano parts he writes. At first I was not for it, but over time I saw his logic and his songs were much easier to learn this way. In the past, I would tune down a half step to help the singer out while also getting a heavier sound from my strings.
Other times, open tunings can give you a whole new sound on the guitar really allow you to explore new territory with minimal chord changing (Ritchie Havens, Jodi Mitchell, etc.). It all depends on the musical situation you are in.
Best of luck, and you can always keep your guitar in standard tuning if you aren't playing along with the original recording. Have fun and keep the questions coming. :cool:
Douglas Showalter
