How often do you enter a sketch, but find it nearly impossible to do anything in it because of all the surrounding clutter (particularly part geometry, other sketches, work planes, etc.)? Sometimes it's almost impossible to see the sketch you're working on, or determine which lines are in the sketch you're working on versus other sketches in the view.
Sometimes, particularly after you've projected in any geometry you need, it would be nice to be able to just hide everything else and only see the sketch you're working on. I propose adding a toggle to do just that.