I've had situations where a migration that ran locally just fine, failed in staging and/or production (config-level stuff running into hosted DB access rights,

I've had situations where a migration that ran locally just fine, failed in staging and/or production (config-level stuff running into hosted DB access rights, etc.). Those situations are a mess to untangle without idempotent migrations. Also, minor niggle but Flyway isn't database-agnostic, you'd have to use the SQL of whatever DB you happen to be using (although if you code in Java I guess you could use ORM commands)