Guitar capo
There are many different types of capos. A nylon string guitar for example has a flat neck, while a steel string guitar neck has a radius. They both require a different kind of capo. Guitarists who like to experiment a little bit more with their music might like partial and third hand capos. They are also discussed below.
A guitar mostly needs some retuning after a capo is added. Some strings wil sound a little bit to high. If your guitar is suddenly very much out of tune, then the capo might be put on to tight. A guitar capo which is not tight enough placed will result in buzzing sounds.

Classical guitars have a flat neck while the necks of western and electric guitars mostly are curved. A round capo used on a nylon string guitar can cause the middle two strings to mute. The other way around, a flat capo on a steel string guitar can cause the outside strings to mute slightly. As you understand, these effects are not desirable.

Partial capo
This capo does not cover all six strings. For example you can use it in a high position covering the high strings, while you still have the possibility to play basses. There are a number of variations of the partial capo, covering two, three or four strings.
Andy McKee often uses one, sometimes in combination with a normal or a second partial capo.

Third Hand capo
This is a great capo for just to play around a little bit. You can put it in a position, and then choose which strings you want it to cover. While playing it is even possible to change this, but that will need some excercise. A Third Hand guitar capo gives you a lot of new combinations.

In the video below you see guitarist Antoine Dufour use a Third Hand capo.