Two subs are always better than one. They extend the soundstage.
This may be true, but for me it is subordinate to them helping with room modes. Two is good, three is great, four is...marginally better.
Helpful:
https://blog.teufelaudio.com/what-are-room-modes/
https://forum.audiogon.com/discussions/subwoofers-and-phase-question-for-you-sub-experts