Here's a handy list for you...

When do you need a zoom lens?
1: When you can't move relative to your subject.

That concludes the list.

Really, a prime lens is superior to a zoom in every way. The only time a zoom shines is when you're stuck in a seat you paid for and your subject is moving around on a stage, track, or court. Zooms can also be nice for things like landscapes and skyscapes, but again, you're somewhat stuck in your seat (where you're standing relative to the heavenly glory you're attempting to capture).