Really if you don't know what it is you don't need it. What problem are you trying to solve? You only set the proxy if you have a controller that cannot be reached without going through another IP address as a middle man. If that's not the problem you are trying to solve then leave it alone.
Thanks for the explanation Gil. I started thinking about this while pondering situation where I have a few controllers I can't 'see' on my home network.
I use a stand alone network for my display. It uses 192.168.2.xxx addresses. My home network uses 192.168.0.xxx addresses.
Oddly enough if I take the cat 5 cable out of my show network/router and plug it into the home network/router I CAN 'see' all my Falcon Controllers but I CAN NOT 'see' my San Devices (E682's). I like accessing the show controllers with my home network computer because it's much easier to make changes than with my show network which I access with my phone.
So...if in XL I enter the IP for the FPP in the FPP proxy column where I use the E682 ports does that the FPP the 'middle man' you're referring to that will allow me to access the E682's with my home network?