1. You have a really high-load system that you need to figure out some clever ways to scale.
2. You're working on a toy project for fun.
If #2, fine, use whatever you want, it's great.
If this is production, or for Work(TM), you need something proven. If you don't know you need this, you don't need it, go with a boring Postgres database and a VM or something.
If you do know you need this, then you're kind of in a bind: It's not really very mature yet, as it's pretty new, and you're probably going to hit a bunch of weird edge cases, which you probably don't really want to have to debug or live with.
So, who are these systems for, in the end? They're so niche that they can't easily mature and be used by lots of serious players, and they're too complex with too many tradeoffs to be used by 99.9% of companies.
The only people I know for sure are the target market for this sort of thing is the developers who see something shiny, build a company (or, worse, build someone else's company) on it, and then regret it pretty soon and move to something else (hopefully much more boring).
Does anyone have more insight on this? I'd love to know.