I always read and hear about people strengthening their PC muscles to help premature ejaculation. Although, I don't know exactly how to tell when they are strengthened.

Men, how do you know when you have sufficiently strengthened your PC muscles? Can you hold your semen in at will, not cumming because you have total control over your ejaculation? Or is this not how it works? Is there another goal. I realize it's a good idea to work the muscles, but don't understand what the end payoff is.