I thought about this a good bit a few years ago when I was putting my system together. My previous couple of systems consisted of floor standing speakers and subwoofers. I think that what @ghdprentice says above is mostly where I’m at now. My floor standing speakers have a 3dB down at 32 Hz, so almost full range and they are setup in a room just a bit wider than @jbuhl mentions above. My REL subwoofers come in at the bottom of their crossover range and add minimally to the overall bottom end. That said, I eliminated the baby REL, because my goal was to only move air down low and I have two subwoofers (more would be better to even out the bass in a medium/small room). Recently, Juan of @blisshifi tuned my system/room. One of the first things that he did was to turn off the subs and to my surprise, what was heard was more musical and with greater clarity. Yup, my subs volume was set too high. I thought the crossover was set at the lowest point, but that might not have been the case. When Juan was done, there was a benefit to the subs, but it was more subtle and they weren’t destroying the lower octaves produced by the main speakers.As an aside, Juan suggested that more subwoofers might be beneficial in my smallish medium size room. When it is all said and done, might I have been better to take the extra money spent on subs and gone with a better speaker? I don’t know, but it was something that I did not consider because I tried to keep cost down at each stage, without looking at the money I would be spending at the back end of the buying process.