It only limits the blast radius on multiusers systems or when people do not follow basic security measures like having a different password on each computer. I agree it is a good one to avoid breaking the system yourself too easily but that is only if you don't blindly copy paste commands with sudo.

The only thing it mitigates really is how easy a malware can hide in the system once already present. But as said earlier once running under your username it is game over, your data is right here ready to be stolen, compromised, altered, destroyed or encrypted.