For the sake of this argument, lets suppose you run a git server. Users $(ssh) into your host and are only allowed to execute the command $(git), for instance for submitting a copy of their repository. You think: It's fine, the user cannot mess up anything on this system since he is restricted to run git.

Allowing any user $(git) access is as powerful as providing the user a $(bash)

Suppose you've got a build pipeline. The pipeline executes $(zip) at some point. Executing zip is as powerful as providing any of the pipelines users a $(bash).