It completely depends on the shot. I find that when I tee the ball up on an iron shot for a par 3 I tend to hit a little farther than if I don’t. So if the shot needs a little less than a particular club I don’t use a tee. If it’s a little long for the needed club I’ll tee it up.
Yes, I tee the ball up on Par 3 holes. Can't understand why this is even a "thing" that comes up constantly on forums. Must be a bunch of very silly people out there thinking a tee under the ball is somehow going to hurt them.
Here's a hint. You can tee the ball on a tee as low as you like...