I have used clickers in the past, but now I just use a marker word which is 'yes'. No particular reason, mainly because my dogs respond well to voice commands and it is one less thing to carry.

It is the same principle as clicker training in that you use a word to mark desirable behaviour and to tell the dog a reward is coming.

I love using clickers/markers and highly recommend it, marking behaviour is a great technique and can make training so much easier as it's such a clear way to communicate with your dog