That's a good question. We are building a "Fort Knox" coop and run this coming spring to go inside our current "sort-of-protected", really semi free range, run. When we do, the plan is to leave the coop door to the run open 24/7 so they can go in and out at will. My thought was, if the run is predator safe, then why do they have to be locked in the coop.
Those are kind of my thoughts too. However, I am newbie, so my expertise is limited.
I still want a pop door though. That way I can either lock them in or out if I need to do maintenance or clean.