When I first started reading about subwoofers the dogma was that one only required one, and many in addition argued that position of the sub relative to the main speakers wasn’t very important. The justification for both of these points was that bass tends to be unidirectional and the low frequency wave forms are difficult to place as to origin in a soundstage.
I quickly learned that the second part of the proposition just isn’t true as sub placement is very critical but I just use one sub in all my systems. The current dogma seems to be use 2 or 4 subs. The systems that I have heard with multiple subs don’t impress me, but their owners don’t tend to listen to the music that I prefer