capos are useful if you're doing standards but you don't have a standard voice. Otherwise I dunno why bother. Yeah, using a capo changes the key. I saw these little half capos this summer and almost got a couple. They fret 3 strings max (but you can choke them up on the edge of the fretboard so they cover just 2 strings). They can fret middle 3 strings too, like skip E and A to fret D G and B if you want. So the idea is, you can quickly have access to certain alternate tunings without actually changing your guitar's tuning, by just moving the half capos around. You could have one on the 2nd fret and the other on the 5th fret or whatever. Looked pretty cool kinda. They were $15 each though, and you sort of had to get a pair. Dopp, you gotta learn scales up the neck that don't use open strings. That frees you up a lot to rock out in whatever key.