One thing that seems to be sometimes overlooked is system databases -- specifically agent jobs in msdb but also IS packages for non-SSISDB packages. Then there are SSISDB, MDS and master and possibly others. What about complex changes that involve instance-level security, for example? Those schemas for those databases may rarely change but the contents can be quite volatile. Actually, the schema for MDS (as well as the data) can also change a lot as new domains and entities and views etc are added.

No good rolling back changes in a user database if packages/projects/jobs/permissions/master data etc. that depend on them don't keep pace.