It depends, really. There is a trade-off in terms of software and operational complexity vs scalability/perf and isolation. And probably a bunch of other factors.

If you have separate databases for each customer, schema migrations can be staged over time. But that means your software backend needs to be able to work with different schemas concurrently. You can also benefit from resilience and isolation guarantees provided by the dbms. On the other hand, having a dbms manage lots of databases can affect perf. Linking between databases can be a minefield, especially w/r/t foreign keys and distributed transactions.

https://docs.microsoft.com/en-us/azure/azure-sql/database/sa...