reasons for using a capo

1. To transpose when the music/chords are familiar in one key, but other instruments/voices need to be in another key.

2. To use tricks, runs, hammers etc. that are straightforward in one set of 'shapes' but not the key that's in use.

3. So two guitars can accompany the same piece with different timbres.

4. As with much flamenco, to use tone changes with shortened strings.

5. Shouldn't happen, but will lower the action if you're playing a lemon.

6. To use closer fret spacing and easier string bends mid-neck.

8. Because you want to stop the melodeons joining in.

9. For particular effects eg partial capos.

10 Because you can if you want to.

Reasons to avoid capos

Dunno, they seem harmless enough.

BTW Chambers Dictionary gives both capotasto and (unusually) capodastro

Stu