Setting alpha to 0 is going to be the same as disabling the game object, but disabling the game object has the added benefit of effectively stopping script execution on all the game objects underneath. The most efficient thing to do that minimizes the time spent in the next two frames is to move the panel off-screen. The downside is that it will still be drawn, just off-screen. The most efficient thing to do for long-term is to disable the game object. So it kind of depends on what you're trying to do.