You have a lovely looking space like @terzinator with Harbeth, which I used up to December 2020 and which benefited with a subwoofer with some music, but subs would ruin his space. He has put in some colour-coded panels, although unless the speakers have no toe-in I would question their benefit.
You then have the hardcore dedicated room approach of @RsZk. I don’t know how many people would have such a space available, probably the minority. It’s a matter of taste, no doubt many people could enjoy such a space, personally I could not. He’s gone to a lot of trouble to get it right, along with measurements.
If in theory I were to get subwoofers, it would be the same REL S/812 that @RsZk uses, but they would be horribly obtrusive and lots of wires.
I suspect these two systems are good examples of the extremes of what people put in their homes. Enjoying music at home is as much about being comfortable in the listening space and the level of domestic compromise necessary. I suspect the reason why Harbeth speakers are so popular is because they tend to sound really good in most rooms without many set-up issues. I’d still have mine if my wife hadn’t hated the sight of them.
I’ve always had to compromise with having cables all bunched up together, power and speaker cables. This seemed to cause some level of interference noise (I was using Sommer cables at the time). Subjectively Townshend cables eliminated that issue and I’ve not given it a second thought since.
I’ve not posted a picture of my layout that I can link. I’ll do one later and it will be apparent that any subwoofer would be horribly obtrusive, let alone four.