For this question, there are usually three tables that most users ask about: the _tmp , _raw and _scd_ tables.
_tmp is safe to delete. If there’s a sync in-progress, it might fail (but should work fine on a retry).
_scd_ is not safe to delete. It’s required for incremental normalization to continue working.
_raw is technically safe to delete (assuming normalization is completing successfully after every sync)