yes, symetry is very good
I got second studio (much bigger, with separate studio and control room, and couple of good mic, RME Octamic II preamps, etc) which we treated with a lot of absorbers/diffusers/bass traps. we have good symetry and acoustics in there, but the studio is 20 miles away, so I'm doing only recording sessions in the studio. most of time im doing mixes/edit,etc in my home where I have Apogee Duet 2.
it would be great to treat my room for mixes so I could work in 2 places with good acoustics.
in the studio we got about 1,2m x 1,7m diffuser on the oposite wall (behind my back when im sitting on chair)
do You guys think that diffuser in my small room will be necessary? im pretty sure that word "standing wave" in my small room is common ;-)