Its not specifically a cpma cvar, and should be left at 0 if you're playing.
Set it to 1, and on startup it'll go off and optimize the AAS data, and create you a new AAS file.
I've not studied it too closely, but the comment at the top of be_aas_optimize.c says that it "decreases the .aas file size after the reachabilities have been calculated, just dumps all the faces, edges and vertexes".
If you're a mapper building AAS files for your maps, you should probably set this to 1 to get the smallest AAS file possible.