Click tracks are insanely useful. As Inconuucl says, it is insanely helpful with things involving samples and tracks. Also a major help when involving non regular band members. You'd be surprised how many bands actually use click tracks. Playing to a click is also a skill that needs practice. Some people are better at it than others.
The good drummers (particularly hip hop drummers these days) know how to really use click for time keeping, but vary from it.
Here's a good demo of how to properly use click. Notice how he varies from being in time with the click to being off. When he is directly on, the counting will disappear, when he is off, you can hear the voice clearly. The actual drumming starts at 2:32. Bonus 13/16 time signature drum solo at the end.
[youtube]http://www.youtube.com/watch?v=Yh8PATuI_NU[/youtube]
Tony Royster Jr. is most well known as the drummer for Jay-Z
D.o.S. wrote:I think it'd be weird if only the drummer used a click.
I have seen many bands play with only the drummer on click, the rest of the band just times themselves to the drummer. A lot of people have somewhat irrational hangups about using click, and that is a happy compromise.