Caffeine can be deactivated from the menu bar with a single click so it could just be the solution to your problem you know... just use it when you need it.

If you have a laptop, you can set your system to never go to sleep when it is connected to the power adapter, and use entirely different settings for when it is on battery mode. That way you have a way to quickly change to sleepless and sleepy mode simply by pulling the power chord.