Is there an ethos with respect to nostr app development?

for example, are developers discouraged from running private backend database instances, in favour of storing as much of their app data on relays, as is possible?

Or is it the reverse? Use nostr as a foundational coordination layer (for identity, payments, etc), then offload the more specific app data into a private database instance, to unburden the relays?

I know it's not a black and white issue, and certain use cases will require certain solutions, but is there a general trend of thought, in this regard?