The value is that rollback stops being an emergency procedure. Reversing a conventional deployment means deploying the previous version and waiting; switching traffic back to a still-running environment takes seconds. That difference changes how willing a team is to release.
The complication is state. Application servers switch cleanly, but databases usually cannot be duplicated per environment, so schema changes must be compatible with both the old and new code simultaneously. That constraint — expand the schema, deploy, then contract in a later release — is the real engineering work behind the pattern.
Codazz builds this in production — CI/CD Pipelines.