In a 172 with full flaps down, I can't believe there's much practical necessity for slipping - even when practicing forced landings. But it's been a looooong time...
But if you have electric flaps, and the fuse blows at an inopportune moment, it's certainly good to have slips in your repertoire. A good confidence-building maneuvre might be to start at 3000', do a left slip for 10 sec., then roll into a right slip for 10 sec., then back to the left, ... Before long you'll be pretty comfortable at it, and develop some precision in holding heading and recovering at a desired altitude.
I've slipped a flapless taildragger down to about 10 feet when landing over an obstacle; once you're comfortable with the maneuver you are better able to handle unusual situations.