You still get the crossover splice optimization which can substantially improve response at the main listening position. Here's an example: https://www.avsforum.com/threads/the-official-dirac-live-thread.3137722/post-60061334
Sure. And I guess that might be worth it in the case where you really can't fit more than 1 sub in the room for whatever reason. But given the costs involved I still don't think it makes sense in very many cases.