We have a use case where we want to slowly introduce this for our users. Also there are other times people are migrating from subversion to git and need to push the object with different users. This effectively blocks them if enabled globally. The first time we enabled it many customers were unhappy because it broke them in the middle of their development and migration. A nice feature would be a dry run mode where it just shows the user an error message but it still allows that persons commit to complete.