Another good use for a capo is to offer an alternate finger shape to play in the key you want. For example, the shape for a normal D is easy to make with 2 fingers (index barring top 3 strings at 2nd fret, with middle finger on the second string in the 3rd fret. Now if the song you want to play is in G, you can capo at the 5th fret, and play the D shape above that. You then have your ring finger and little finger free to do other things, to liven the tune. This would can be more versatile than playing an open G in the first position. Ian Anderson (Jethro Tull) does this a fair bit.
A trigger-style capo can also be used to do an instant "drop E" tuning, by capoing the top 5 strings at the second fret (capo upside down) leaving the bottom E string open. Bruce Cockburn and Tom Cochrane do this on occasion.
It's a nice simple tool that can add options to a lot of tunes. Have fun experimenting with it, because your imagination is really the only limitation.