sometimes a program asks a lot of questions, and you know you want to answer all with yes.

if there are 200 questions it'll take a while. Pipe the output of the yes command to your program to automatically answer yes to all questions:

$yes | rm -I *

this particular example is of no use, but demonstrates it's function. rm -I * removes all contents of current directory interactively (asking if your sure)
sometimes rm is an alias for rm -I but even then you can just use rm -f (force)

There are many cases where the yes command could be of use.