Having to write and perform migrations for every small schema change is a bore, but it means your software doesn't have to worry about handling different versions of data. Going "schemaless" with version numbers means moving code from "write-and-forget" migrations to the main codebase, where it will live forever.
I think not doing database migrations only makes sense when you can make do without version numbers (or if you can't do atomic migrations due to performance constraints, but that's only a problem for a very small number of projects).