Not necessary for stock gameplay. Used to install the Unofficial patch, Killer App Mod, the map pack and Error 1 & 2 fan-made campaigns. https://steamcommunity.com/sharedfiles/filedetails/?id=325088441

The game runs fine without tinkering, still, KA mod recommended for widescreen support, bug fixes and more.

Multiplayer server list fix. Add those system-wide to your /etc/hosts

65.112.87.186 tron20.master.gamespy.com
65.112.87.186 tron20.ms9.gamespy.com