This is a file that you need to place in "C:\Program Files\Steam\SteamApps\common\Team Fortress 2\tf\cfg" if you have an aging PC. It will make sure you have even lower graphics than you can set in the TF2 menu
There's no new setting, it just puts your graphics to lower than "Low". Which is useful if you're on an old computer. Also, here's a website where you can build your own (it's kinda better than that autoexec.cfg I posted): http://clugu.com/tf2mate/