We are probably all little people here, and nothing like this would ever happen, but say you were high profile enough like that Google self-driving guy that Uber poached, and there was a lawsuit - anything you did on that computer would be up for grabs. All your personal projects, documentation, DMs.. it would be super messy. I’m pretty sure companies like having this kind of situation because it gives them legal ammo in the rare case where there is an action.
Let me ask you one follow up question: if you and the company had a disagreement of sorts and they examined your activity, would you believe they find nothing that they’d deem privileged?
I’m now understanding how people get sued when going from company to company.