Why? Because I just bought the software and I'm learning how it works and how to use it and I'm running some experiments. I wanted to create one, many actually, user groups the same as a template group I created, one for each US state. I looked for a function to crank out uniquely named clones, didn't see one so I asked on here if such a thing existed.
If I create a group 'state' and want to make 'state 1', state 2', ... it would be nice to duplicate or clone a template group with a click and set a unique name but with everything else the same with a simple, dialog. click, type, click type, etc. Was that a foolish question to ask or is that feature hidden to prevent abuse?
That is a good post you reference. It outlines exactly what I'm trying to do. The same or similar is in the permissions help link on the permissions page.
His "why" comment was really just to indicate that duplicating permissions across groups is a sign that it's not an ideal group setup. Using you're example, you would likely setup the base permissions shared by all groups in one and then add permissions for the specific groups as necessary. The significance being that if the permissions change (or a new permission is added from an add-on or the core), you don't need to repeat the same action 50 times.