A benefit mentioned already that I like is that since there are concrete walls already (at least on any walls that are at the exterior of the house) it is pretty easy to "float your wall" since you need to build walls anyway to hang drywall and such, you can just put them an inch away from the concrete wall and do other accoustic treatments to isolate the room from the rest of the house. That is also where it is easier to build a front stage (filled with sand) to create a barrier between front speakers/subs and the concrete floor without wondering if all of that sand will weigh too much....
