No, screen lock is just the screen you go to when you turn on the screen with the power button. You can still have the screen turn off after a certain time, and anyway it will turn off if you hit the power button. By disabling the screen lock, you can go straight to the home screen, or running app or whatever. Especially useful in the car.
While we're on the subject, everyone check out extended controls, its pretty nice. A customizable replacement for the stock controls widget thatyou can set a shortcut to in the notification menu. I wish the controls themselves could be set there though. Anyone know a widget that does that?