>>394909496
When you can't maintain FPS, your display will drop to an integer quotient of your refresh.

144 > 72 > 36 > 18 > 9
120 > 60 > 30 > 15 > 7.5
90 > 45 > 22.5

etc.

If you can maintain 60 but not 72, you want to be set to 120 or 90hz, so your framerate doesn't drop to 36.