Windows Hardware Accelerated GPU Scheduling added in May of 2020 is not an fps booster or magic switch, so I was unsure why there is so many benchmarks showing performance with it enabled and disabled without any other strain on the system comparing frame times and stability. The gains and losses in a real world scenario are pretty much invisible and could even be blamed on some completely different variable. In my opinion in real world cases it just is what it is, prioritization of gpu usage to a game in particular. It mainly just ensures the game you are playing receives graphical power first and everything else second, similar to setting your Routers QoS (quality of service). Many apps such as Discord, Spotify, Chrome, OBS, SteamUI, In-Game Overlays and even the Window Desktop Composition... all use gpu acceleration these days. So, this scheduling is particularly useful for streamers or someone using some of the apps previously stated while you play. You can disable hardware acceleration in pretty much all of them, just google how because they use anywhere from 2-20% gpu usage. Keep in mind disabling hardware acceleration will force the application to fall back to only CPU. If you do not use multiple apps while you are playing it seems disabling gpu scheduling is the preferred choice. You can pull up the gpu scheduling settings page by typing GPU in the taskbar search box, add each game at the bottom.
As for what it does to cpu usage isn't exactly noticeable yet but I'd like to see it latch a game to a set or cores and isolate itself from other processes & tasks similar to what you can achieve with Prio.