Usefulness of db migrations rollback

Question

Many people talking about db migrations, especially about its rollback possibility.

I doubt, whether it is useful at all, because schema of db and model are tightly connected with application logic (MVC).

Suppose i've done rollback of some migration. And what ? The application will not work, because its logic fully relies on db.

What are the use cases of rollback ability for db migrations ?

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Update 1

The main question

Why the rollback is presented as a feature, when i need to change the code ?

I don't create the migrations, like "add_another_field_to_table". Instead, each migration file fully describes each table in DB. When i need to change something in my DB, i just change the migration file, but don't roll it back.

Really, if i rollback the migration, it does't brings me back in time, like a version control does. I have a lot of work, when changes are planned and rollback gives me nothing.

Answer 1

The point of rollback is that you rollback code and DB at the same time. The scenario is you upgrade your code and your DB on your production server, then you find a bug and you really need to go back. So rollback your code and use your down migration to roll back your DB.