It forces you to resolve conflicts. Two developers create a migration on the same day, but they get merged later. Alembic stops you and ask which goes first. A

It forces you to resolve conflicts. Two developers create a migration on the same day, but they get merged later. Alembic stops you and ask which goes first. ActiveRecord::Migration runs them both. This is particularly bad when one migration is a table drop and another is an add_column on the same table. And that's just one short coming. Our monkey patched ActiveRecord::Migration doesn't do this (yet), but we've done quite a few other improvements to it. Another significant difference is the migration generation. Once you've generated migrations with alembic, it's hard to tolerate anything else.