Page loading times, general stability. Everything, really.
I set it up with sqlite initially to test if it was for me, and was surprised how flaky it felt given how highly people spoke about it. I'm really glad I tried with postgres instead of just tearing it down. But my experience is highly anecdotal, of course.
This is the setup I have (Nextcloud, Keepass Desktop, Keepass2android+webdav) and k2a handles file discrepancies very well. I always pick "merge" when it is informing me of a conflict on save. Have been using it like that for years without a problem.
Edit: added benefit, I have the Keepass extension installed in my Nextcloud, so as long as I can gain access to it, I have access to my passwords, no devices needed.