if you don't have an event that checks the collision, then you don't need to worry about it. There are no collision checks that are performed.
say you have 100 balls floating in/out of your layout. and everytime your player hits them, they pop. you have to have a statement that says if Player On Collision with Ball. This creates lots of collision checks.
However, if you for some reason, set all the Ball's collision properties to disabled, then that trigger will not happen and not checks are done. Or more constructively, if you set just the balls that are off screen to disabled then you are eliminating unneeded checks i.e. since your player is always in the center of the screen it will never collide with something off screen.
If you have a sprite that is background art and never needs any collision check. You don't need to turn off collisions because you don't have any events for it.