Seriously. For all the gripes that everyone has for team arena, it's really some cool stuff in there.
It's a key/value of the gametype that allows things to spawn in modes.
Like say you had a func_static bridge, and only wanted it to spawn in ctf. Well, you add the key gametype and the value ctf.
If you wanted it to only spawn in either ctf, commandpoint, but not oneflag, you would add
gametype
commandpoint ctf
and that's it. you could also add that into the worldspawn to keep people from firing up the level in ffa and teamdm, etc.