One of the features of the Windows 10 Game Mode is that it raises the thread priority of the application. This proved incredibly useful for me in some games - most notably GTA 5 - and in a lot of other games it didn't seem to do anything at all. I'm pretty thankful for the feature - because manually raising the thread priority every time I open the application was a very unnecessary pain.

Is it the "Game Mode" that enables the Xbox DVR by default? If so, it did do something, it locked my FPS at 30.

It is such a big problem that Valve had to build in detection into their game where they warn you about it.

And in order to turn it off, you either have to login to their Xbox App, or play around with regedit, Valve have documented it here: https://support.steampowered.com/kb_article.php?ref=6239-DZC...

And it seems like updates are enabling it again automatically, because I have had to do it twice.

It probably only works if you have a ton of random shit installed and running in the b/g - which isn't most reviewers, but is most users.