If you've upgraded Windows 10 to version 1903 (May 2019 update), you may have subsequently noticed a new variable refresh rate (VRR) option in the graphics settings menu. Microsoft added the toggle to force games that do not support VRR to use the feature anyway.
AMD (FreeSync/Adaptive Sync) and Nvidia (G-Sync) have been pushing VRR implementations for quite some time now. For anyone who is unfamiliar, the short version is that it syncs the refresh rate of your monitor with your graphics, to eliminate screen tearing and stutter that can otherwise occur. It keeps the action smooth, just as the gaming gods always intended.
Microsoft's toggle seems redundant, and quite frankly, I'm not 100 percent sure where it would come into play. In a developer blog post (opens in new tab), Microsoft program manager Daniel Schlegel explains that it enables support for DirectX 11 games in full-screen mode where VRR is is not natively supported.
"This new OS support is only to augment these experiences and does not replace them. You should continue to use G-Sync/ Adaptive-Sync normally. This toggle doesn’t override any of the settings you’ve already configured in the G-Sync or Adaptive-Sync control panels," Schlegel explains.
I have never run into any issues using G-Sync or FreeSync. However, according to this Reddit post, Windows Store games were initially not compatible with VRR. Microsoft later added support, but it had to be implemented by the developer. Apparently there remain some games in the Windows Store that still don't.
That is where this toggle would come into play, presumably—it acts as an override. You will only see the option if (A) you have Windows 10 version 1903 installed, (B) own a G-Sync or Adaptive Sync monitor, and (C) are using a GPU with WDDM 2.6 above drivers that support G-Sync or Adaptive Sync. Even then, it's not a given—I meet those requirements, and the option is not showing up.
If this is an issue you have run into with DX11 games and you see the new toggle in the Graphics settings menu, by all means, try it out (it's disabled by default). There's no guarantee it will work, though. Schlegal says there could be "unexpected issues while gaming," in which case you should flip the toggle off again.
As for where else this new switch might prove beneficial, I've reached out to Microsoft for comment and will update this article if and when I hear back.