Ports tab left checkbox?

[GABB]

I can't figure out what the leftmost column of checkboxes do in the Ports tab. Checking one next to a port has no apparent effect. Checking the master one at the top creates what looks like an "extra" port to be filled in at the top, and I have no clue what that indicates.

[lligetfa]

It allows you to make mass changes on all selected ports.