I don't often use one, but I wouldn't hesitate to use one in the right context.
Too often capos get a bad rap as a "cheating" tool. This is absolutely false.
The main benefit of a capo is to preserve the chord voicing in a different key. Sometimes, those who misunderstand the purpose of a capo will think you can just use barre chords instead. But, depending on the context, a barre chord may alter the chord voicing, which can negatively affect voice leading and the underlying harmony of a piece.
When I use a capo, I most often use it with acoustic, but I have occasionally employed one for electric.
I don't like the kind with the spring, though. They run the risk of pulling the strings sharp because they clamp pretty tightly. They are also fairly bulky. I do have one of those, but I use it to hold strings in place when I restring a guitar with a Bigsby!
I use the kind shown below. This kind is better because you can adjust the tension with the thumb screw. This allows you to adjust it just as tightly as you need it, without clamping too tightly. It also is less obtrusive and weighs a lot less. It's less likely to get in the way of your fretting hand.
