If you're running Nvidia, it includes the official drivers OOTB and keeps them updated. There's also stuff like WINE and Lutris already included, udev rules to make sure all controllers just work. For handhelds or home theatre PCs it includes gamescope and will boot straight into gamemode/big picture mode without the DE loaded, saving resources. There's lower level stuff as well, like a modified kernel that makes things faster, kmods for AMD APUs so you can adjust the TDP properly, scripts for setting up things like Sunshine easily. It's also immutable, which is great for gaming because if anything breaks on an update, you can easily reboot back into the previous version in minutes and get to gaming without eating limited gaming time troubleshooting or downgrading stuff.

I have it installed on one of the original Lenovo Legion Go's and it makes it indistinguishable from a Steam Deck in function. Even with SteamOS getting a wider release now, it still offers a bunch of advantages.