When I make a change to a program or in Control Panel, should I hit “Apply” before “OK” or is just “OK” fine?
Hitting OK will apply the changes that you want made, so you don’t need to hit “Apply” first.
Where Apply comes in handy is when you are making a change to your desktop (theme, color scheme) or Display Properties (screen resolution, color quality) and you want to check the result without exiting out of the control.
Another time when you could use Apply is if you want to make multiple changes in a particular area but want to test the affect of each before proceeding.
Some people just feel more secure hitting Apply before OK. If this is you, then click away.