The computer is another thing indeed.
I'm not concerned about what's on there, but more for someone accidentally messing things up.
And in all honesty, I rather not have anyone else on my PC. It's called PERSONAL computer after all :)
So much is on my PC, although all that matters is backed up on an external HD, but the way I've organised things might be totally illogical to another and I do not want it changed.
And I sure as heck don't want anyone to mess with the basics of my PC. If it doesn't work anymore... I need it too much, I do everything on it.
When still living with my ex I was okay with him doing stuff as he wouldn't screw up: he'd be the one that had to fix it again
My son once changed some settings on my phone, went home, and my phone did different things then. I had no idea what he'd done nor where to find these settings, haha. He's way more savvy than I am with these things (with PCs as well).
So I had to phone him to undo it and ask him to never change anything again without asking and telling me what.