When can you select Final in Process Configuration

I'm setting up and modifying a new project area based on an extracted process template. I can't seem to make my permissions Final so they can't be overridden in child Team Areas. The checkbox is grayed out in the Project Area permission menus as well as in the process template and the original project area where I extracted the template from.

Can someone help me understand the rules on when you can select this or modify this setting? I can't seem to find anything in the forum, articles or the Infocenter.

Thanks in advance.