This strategy allows to pick the preferred strategy given the current platform. It allows full portability because you are guaranteed to have a working strategy no matter which RDBMS you use.

The issue is that a given strategy might be optimal at some point in time, then letter better strategies emerge.

For instance, for PostgreSQL, AUTO translates to using sequences, but, as mentioned in doctrine/dbal#5614 , that might no longer be the best strategy.

Since we cannot really release a new major version of the ORM every time this happens, I suggest we deprecate the AUTO strategy and let people explicitly pick one.

The obvious drawback is that full portability is lost.