I don’t use GSX. That’s the reason I initially asked. Umberto says he answered me in another thread but he is imagining things as he most certainly has me confused with someone else.
I'm not "imagining things", and I not obviously confusing you with somebody else, since I DID made a proper reply to your other post in the General section but, for some reason ( possibly related to the fact I was in vacation with a spotty Wi-fi connection in my Hotel ), I just noticed now my answer disappeared.
My disappeared post explained what GSX/Couatl is used for in our sceneries that use it and, right now, it's basically mostly the VGDS systems. If the reasoning of your question was to know if GSX/Couatl is "mandatory" to use a scenery, it really depends how much value you put in that feature.
For me, a scenery like KORD, KCLT, LSZH, which contains dozen or even hundreds ( in case of KORD ) of VGDS, is seriously crippled without GSX because, instead of the proper VGDS, you will only get the default MSFS Marshaller.
But again, only you can decide if the completely zero impact of Couatl "running in the background" with the addition how much easier is to Quit/Restart it in MSFS, is worth to lose VGDS. And of course, we might likely add other features, because before GSX came out, all these airports had extra features we lost when we moved them to MSFS, which were all obtained with Couatl/GSX.
Of course, just like FSX/P3D, using GSX in an FSDT scenery is free: if you have an active license of ANY FSDT scenery, you can install GSX without an activation key, so it will work on all FSDT airports in full, plus 3 extra Trial airports. By purchasing GSX for MSFS, you'll be able to use it everywhere.