When I clone a new project, I put the proper email address (e.g., a company email) as an author email in the local config stored in the repository. It worked fine until I started working for a client whose project is spread across many repositories that I cloned when needed.
I can’t count how many times I forgot to put the correct email into the local config of the newly cloned repository before committing anything into it – just because I was in a rush. In effect, my personal email (which occupies my global configuration) has been leaking many times into commits, sentenced to last forever in the git history. I’ve probably done it more times than I even realize.
To avoid making these mistakes, don’t use a global git configuration for identity.