In my opinion HENRY53 is offering the best and simplest answer and I am hesitant to try to expound. God gave us TWO ears on the side of our head and a brain that can detect minute differences in the timing of sound. A voice arrives a millisecond earlier to one ear and our brain can instantly locate the voice in the dark. Some sounds reflect or bounce of surfaces and others are more likely to get absorbed and diminish. Moving the speakers off the reflective surface of the back wall and side walls allows for better timing of the sound arriving to our ears. There are a ton of other considerations such as low frequencies attenuating in corners or even canceling out. That's why i agree when people advise to experiment with location and angles.
Why does pulling out main speakers from wall improve sound?
Ask my dealer this question and he was stumped. He said it's a good idea but couldn't say why. I see speakers pulled out eight or more feet from the wall in very nice systems.
The drivers are facing forward, and when there are no ports in the back of the speaker so why would it matter?