Room treatments are largely a futile endeavor. You should never try and make a room dead. The problem people are trying to correct is as usual poor speakers. Specifically the problem is the off axis response not matching the axis response. Occasionally a rear wall may need some attention to curb slap echo.
Acoustical room treatments aren't generally used for making a room dead, they're used to limit reflection time in order to make speech intelligible and to allow the perceived location of sounds to be correct or to come close to matching their locations in the mixing/mastering room. While it's almost impossible to truly match that sound, coming close is a goal some people choose, for better or worse.
The first reflections in narrow/small rooms cause a lot of problems, especially when the walls are similar or the same length. If that room has hard surfaces, it's very hard to achieve good sound, never mind great sound. High SPL compounds the problems and equalization will never tame them. Flutter echo is a bad problem in small rooms and if nothing is done, nobody will enjoy the experience. It's easy to hear flutter- walk into a room and clap your hands- it's very easy to hear and any sound of impacts in music or sound form videos will show it. This also emphasizes the frequencies that reflect most and when they're in the range where people are most sensitive, the level can be decreased using EQ, but the duration can't be adjusted using any controls in the equipment. Slightly lower SPL in those frequencies will decrease the duration to some extent but that can't be considered a 'cure'.
Go into a lecture hall that hasn't been treated and try to understand what is being said, then treat it- huge difference. Restaurants are a prime example of spaces that should be treated, whether they have music or not.
Anyone who has been in a place that has terrible acoustics may find that their mood changed after they spent time there- noise levels and bad acoustics are often called 'sonic pollution' and after having dinner at a restaurant last night, I can give you another specific example of this- we were in a small booth with less than 4' between any of us and it was very hard to understand what was being said. We could, however, hear people across the room very clearly because of the 45° angles of the ceiling causing the sound to reflect directly to our booth. The din was very annoying. Open concept houses with high ceilings suffer from this, too. Without treatment, home theater or even dinner, would be a terrible experience.
