I do use a single sub with my AVR. For my stereo, no sub. And there are several whys involved.
First, it's a main room in the house, so I take down the speakers between use. Did I want to have to move my sub as well, and re-cable every time? No.
Second, I have an INSANE amount of room gain from a vertically compliant floor (soft, bouncy, lively, whatever). So it acts as a passive radiator. Lots of additional gain in the bass and infrasound. Knowing this I got Sierra LX speakers. I get flat to 30 with them with EQ... 5' off the wall behind them. The bass below 35 is not great, but not super bloated either at my normal listening volumes. And if I turn them up, the house will shake. Thank you 100 year old floor!
Third, subs tend to energize my floor more, being near the floor and on the floor. Even with isolation. And floor energy is my enemy.
Fourth, my goal with this system was simple, not perfection. I have played around with a lot of different configurations, I wanted something that was simple and effective. This is. Stunningly good in the triangle spot, and nice everywhere in the room and the rest of the house for that matter. And once I can open some windows in warmer weather, it will be better.
A sub would let me pull the LXs out 4' more into the room and get a deeper sound stage, based on experience. Eventually I will get something to allow that, but currently I would have to use my sub for the high pass, and I am not thrilled with the sound when I do that (SVS SB1000). I would only do that the few times a year my wife is out of town so I can leave them set up, since the right speaker would block her view of the TV.