If you want to disable it to save memory, don't waste any time and effort having to enabling-disabling it, because the whole GSX code runs entirely outside FSX, under another process, so it uses its own separate VAS space and won't take a bit of memory from FSX.
For similar reasons, if you want to disable it to save fps, you won't see any change, if you are not using it, because if you are not on ground, GSX is sitting idling without doing anything, save for checking if end up on an airport, and even this code won't affect fps at all, because it's running outside FSX, and so it's being scheduled by Windows to use CPU power from one of the unused spare cores, and you have plenty of it, when FSX is not loading a new scenery.
It's only when it starts to "create" visible stuff (vehicles, humans, etc.) that GSX has the ability to affect either fps or memory, because of the object added, that affect your performances in a similar way as having 3-4 AI airplanes more. But of course, this doesn't happen until you called GSX and asked for a service.
The only reason you would want to "disable" GSX, is if you want to use a different ground support product on a specific airport, in that case there's an explanation on the manual how to create a list of disabled airports, so GSX won't work there.
