Ask HN: Application level sharding and stateful services?

Does anyone employ scaling your apps via stateful services via application level sharding (i.e. using Akka)?

Here are some claims: https://www.youtube.com/watch?v=CiVsKjZV-Ys

To me it seems it's much better to keep state in (sharded) DB rather than shard on your own in application level, but I'm happy to learn more. Do you know of any literature/blogs on this?