Does this one have a purpose?
Well, yes. It allows people who want pattern signatures that do not bind to have pattern signatures that do not bind.
Given that it is easy to specify, and easy to implement, I'm inclined to give them their wishes.
Having lots of combinations be possible (for users who care to specify them), as GHC has historically done, is fully compatible with language editions that embody a particular set of choices. I like language editions, but I don't see them as a reason to restrict choice.
(If it was hard to implement something that would be a strike against choice; but that's not at issue here.)
I don't think this particular issue is worth burning many cycles over :-). Let's just accept and move on.
Simon