Warp Vote Functions..When are they useful?

__any(), __all(), __ballot()

What type of situation merits the use of these functions?

I understand what they are supposed to do, but would like to see a working example to get a better idea of when they could be used.

Do they really speed up a reduction/scan?

I have an “indirect” experience with warp vote functions, as I was considering to use them in the past.

Concerning __ballot, you may wish to take a look at my (the second) answer to the post

http://stackoverflow.com/questions/10557254/about-warp-voting-function