HAGS worked ok for me specifically in MSFS over the last few driver/windows/sim updates but destroyed performance in a couple of my other most played games, especially if I was using motion smoothing. Bit of a pain when it requires rebooting to enable/disable and the benefits in MSFS weren’t noticeable so left it off.
It seems there were (or maybe still are, haven’t tested it yet) serious compatibility issues between using HAGS and WMR motion vector smoothing at the same time… at least in some games. With HAGS off those games would get a beautifully stable 45fps reprojecting smoothly to 90. Without changing anything else HAGS on would result in bouncing all the way around from 30-60 with relatively low GPU usage at the lower ends which needless to say wasn’t much fun. It also used to cause me to drop to around 70fps in AMS2 with less than optimal GPU usage, while turning it off would maintain 90 and come close to maxing out the GPU.
Will definitely be giving it a go now I’m on the new update, but if you ever have issues with low GPU usage (and of course no corresponding CPU bottleneck to explain it) or issues with reprojection stability I’d recommend visiting the HAGS option as step one of any troubleshooting!
EDIT - just went up for a spin with HAGS on, can’t say I noticed any change… yet to try it in the previously problematic games.