A free speed boost for your active (the one that visible) application.
By default, Windows allocates equal system resources to every program you're running. If you have a few programs going at the same time, the one you're focusing on isn't operating as quickly as it could.
Windows does include tools to adjust program priority, but it's a tedious, complicated process. This download can automatically set your active window to a higher system priority.
It basically checks every second or so to see which window is active at the moment. It sets that window at a higher priority so your computing power is focused on what you're actually doing from second to second.