My room isn't very big but that didn't stop it from having some problems that made me crazy- at my listening position, I could hear the difference in response when I moved my head to either side, only a few inches. If I sat in the 'wrong' position, I hated the low end and it really annoyed me. I decided to try using some panels I had made for a home theater that also had a large dip in the response around the same frequency and ran REW, to watch in real time as they might/might not help. They did and I haven't made any changes to the room since that time. I don't want or need 20Hz response (I did car audio for a long time and at times, super low frequencies can be annoying, to me) and the response is very smooth with the -3dB around 38Hz but excessive reflections and reverberation don't do the system/music any favors. I can feel the floor vibrating at times, even in a different room and that doesn't require extreme SPL.
I installed a small theater in the basement of an old house that has masonry foundation, mortered plaster on the walls and a Terrazzo floor. I walked in and said "Oh, my god!" when I heard the, let's call it 'ambience'. I measured the RT60 and the app showed that at some frequencies, it was as long as 6 seconds. The homeowner was all for treatments, then his wife entered the equation and 'they' (meaning 'she') decided to turn the theater area 90 degrees to the left, so I decided that it would be best to do what I could without arguing and trying to be pragmatic with people who don't actually care about acoustics. Fortunately, they had a large area rug and a huge pit group that absorbed the sound and prevented it reaching the back walls. It actually sounded pretty good.
I'm glad I took that acoustics class in college- it really helps to know what's happening and provides a good basis for solutions. Industry pros can be a great resource, too.