I saw the Grateful Dead play in front of their wall of sound in Vancouver, B.C. in 1973. It was amazing. And quickly abandoned because it was so expensive to set up and transport (they had to have two sets leapfrogging each other on the tour).
It just sounded phenomenal. Apparently one reason bands play so loud is that loud music overrides some of the delays and muddiness in sound. Because the wall was so clear, they didn't need volume. And the many speakers covered any hall or stadium with a gigantic wave of clear sound. They didn't need to turn it up to 11.
"The Grateful Dead sound system is really 11 independent systems or channels as shown in the table below. The source of sound are located behind and above the performers so they hear what the audience hears. Only one source location for each channel is used to cover the entire hall and the music is clearer both on stage and in the audience. The stereo effect is very satisfying and natural to persons all over the hall. Intermodulation distortion between instruments is of course non-existent." - from http://www.dozin.com/wallofsound/#