My question is, do I leave them both enabled?
No. You don't "
have" to. But you can if you want to.
I say, try it both ways. It will not harm anything, one way or another. Then see if you notice any improvement one way or another. I doubt you will since both do very much the same thing - just in different ways.
Having said that, Freesync is [more or less] "open source" and free. That is, monitor makers do not have to pay royalties to AMD to integrate it into their monitors. G-Sync is proprietary and not free - monitor makers have to pay a licensing fee to NVIDIA to include it.
This is similar to Sony and Blu-ray, the rights of which Sony owns. If a company wants to include Blu-ray support into their product, they have to pay Sony a licensing fee for each license used. Note this is exactly why Windows does not include native Blu-ray support; Microsoft would have to pay Sony a fee for each and every Windows license. And that fee, naturally, would increase the cost of a Windows license for every Windows user out there, regardless if they have a Blu-ray disc player in their computer, or not. Since most users do not need Blu-ray support, Microsoft wisely chose not to include it.
If the consumer wants to add Blu-ray support to their computers, the required licensing fee to Sony is paid by us in the purchase price of the Blu-ray disc player.
So, my point is, if your monitor supports G-Sync, you paid extra for that support. And if you have a NVIDIA card that supports G-Sync, why not use G-Sync?
If me, if I had a NVIDIA card in my PC and a monitor (or monitors) that supports both G-Sync and Freesync, and since there really is no advantage to have both enabled at the same time, I would probably disable Freesync if it was enabled by default.
On a laptop, however, if I traveled a lot and frequently used my laptop with different external monitors, TVs and/or projectors, I probably would keep both enabled (if I had the option) to ensure, regardless the type of display I connected to, I would still have the necessary tools (adaptive sync or variable refresh rate) to prevent (or at least minimize) screen tearing wherever I went.
G-Sync is not mentioned at all in the specs. I find it mentioned only once on the Overview page where it simply says,