What you need are some use cases. Imagine going to a website that had some JS that could read memory of that browser process. I'm not sure what's in Chrome's memory and the process is shared (without site isolation enabled) by iframes and referring pages and what not IIRC.

But basically, imagine you could go to a certain website and they could open bankofamerica.com in a hidden frame and if you were logged in, they could possibly find spots in memory that had that site's information. Or Google, or Facebook, or whatever. Could be worse depending upon how Chrome's password manager stores passwords in memory.