Amphetamine keeps your Windows from going to sleep.
The sleep mode is default set to 30 minutes in Windows, sometimes you're downloading, converting, burning, streaming or performing some other task that requires your computer to be awake, sometimes the program in question doesn't do it on its own. For those situations, Amphetamine will keep your computer running for as long as the app is open. You don't need to change system settings every time with the app.
To get back your beloved sleep mode just close the app and voila, your computer can sleep again.