One benefit is you can have different branch restrictions. Staging can be less strict (e.g. allow merging even if test suite is failing while master can have stricter requirements, like no merging unless tests are passing.

Or only require code owner approval on staging->master (or only requiring code owner approval on merging to staging)

I’m sure there are ways to accomplish the same sort of thing with tags, I’m not hugely tied to this workflow (other than it seems to work for our team)