Yes - beneficial, although it doesn't fix everything.
Being hacked through your browser is one of the most common ways you'll be hit. If the browser is running as a user that doesn't have access to your private files, your web cam and such, then the impact of a hack is much less.
There are still risks. If the hacker uses a local privilege escalation exploit, they can bypass the sandbox. Depending on how the sandbox is done, the hacker may get access to all you web traffic - and steal all your cookies. And this does nothing to protect you against phishing and other attacks.
In fact, this is such a good idea that many browsers do a similar thing anyway: the browser sandbox. Off the top of my head, Chrome does it on Windows and Linux, Firefox does it on Windows only. Some Linux distributions have an AppArmor profile for Firefox that achieves a similar result.
If you're keen, take a look at Qubes OS.