For some things, yes I suppose it would be "good" to leave your side panel off. A situation would be if you are having temperature problems and are using an outside fan or something to diagnose and solve a problem. Another would be if you were perhaps overclocking and trying to see your personal best benchmark or something to that extent. Other than that, the extra dust build up that having the side panel off and the obvious risks of something falling inside and harming components present might not be worth the few degrees you would gain. But I guess that would be a personal decision and would warrant a safe area preferably off the ground to keep your side panel off.