It's a separate program from the main resident tray tool so it takes up no resources during normal operation.
It's main purpose is obviously to help you configure ProcessTamer and create rules, but it will also let you view and change priorities on the fly quicker than through task manager, etc..
You can see that the new gui has 2 tabs, one is configuration of options and explicit override rules,
and the other acts as a kind of quick-access task manager where you can manually change priorities or kill processes.
note that this gui for configuring is a completely separate exe that is invoked when needed, so that the main program running in the tray remains super small and efficient.