I for myself never understood the difference and, unwilling to dive deep in the documentation, always opted to mark nothing and let the system to figure out.
I guess is not the best option but I really can't see the difference, except the physical location.

My two cents,

On Fri, 2017-04-07 at 22:09 +0200, Lars Seipel wrote:
It's only mildly better than putting up a message that says "we want you
to take a deep dive into the documentation, NOW".