That main goal is to get as flat as response as possible, but bringing up the nulls, and taming the peaks. I would recommend you read this
http://www.ethanwiner.com/acoustics.html There are tons and tons of research out there done in professional laboritories showing the success of RF, Mineral Wool, and similar products. Why else would expert sound engineers use them in their studios.
You do not want a room that sounds to dead, but that would only happen if you treated every square inch of all your walls/ceilings. Is misunderstood the 38% guidline. The best place to sit is 38% from the back wall, not your speakers. The second best place to sit is 38% from the back wall, if the 1st option is not available. Sitting 50% from the front/rear walls is bad, and along the rear wall also. These locations are where bass likes to accummulate.
Again, the goal is to get as flat as response as possible, reduce comb filtering, and improve peaks and nulls. Spend some time reading the articles on Realtraps.com and watching the videos if you have broadband.
For me the sound improvement is very much noticeable, it was well worth the project and cheap cost. By the way, the bass in my room and sub LFE has tightened and much improved as well. I can distinguish the different notes easier, instead of having ONE Note Bass, as many experience with their subs.
