User privilege separation is a foundation that allows many container implementations to work, and for sandboxes software like Tor or, for however unlikely it is that you're running atop on it, Android use, etc.

If someone is running Tor to not end up in prison/dead, their Tor sandbox can be opened for anyone to own, for example.

Root privileges allow for a much wider attack surface for escaping out of a VM. Not using root everywhere still helps with defense in depth.