Most of us set our computers to sleep after 10 minutes or so, but there are times you need it to stay up longer, e.g, while downloading Windows 10. Don't Sleep does exactly that for you!
You may even enable its timer to let it exit by itself after, say, 30 minutes or 1 hour. Cannot be any more handy.
If your laptop/tablet is Connected Standby type, you should select "Screenserver / turn off monitor" in addition to standby, because they go into sleep as soon as the screen is off.