I've posted on this before, including today in another thread. I agree completely with Siegfried Linkwitz. My room treatments are entirely carpet and furnishings. In fact I go out of my way to add windows and reflections. Most domestic rooms have reflections within the 40ms Haas fusion zone. As Aservi points out these are necessary. Dead rooms sound much worse than live ones. Very few domestic rooms have a reverb time out to 1 sec.
Even if a room does have a reverb time long enough to hear a perceived echo, more often than not they still sound very good. My lower level living room is one such room and it sounds very good.
The problem is speaker problems. If you feel a need for room treatment, it usually means a shouty speaker, and there are loads of them, and a speaker where the off axis response does not mirror the axis response.
I have never felt the need to plaster objects on my walls. Also I use TL speakers which seem to not set up boom. They couple well to the room a give very even bass coverage throughout the space. I'm certain I could only degrade my room with treatments. If anything my theater is a little on the dead side despite significant reflective surfaces.
