Back in WoD, I used Provinggrounds Gold as Requirement for my Groups.
And even now I take Proving grounds into Consideration. If someone doesnt have ProvingGrounds, RIO, nor Logs, hes a complete wildcard.
He can perform anywhere between 5K DPS and 120K DPS.
So if I see someone with only Bronze Proving Grounds, that tells me that at least at some point he wasnt good enough for even Heroic Dungeons. Doesnt tell me he is it now, but its an Indicator. So Obviously it affects my likelyhood of Inviting him negativly.
Someone with Gold is more likely to get an Invite.
I would really welcome having the Proving Grounds mandatory again like in WoD.
The Threshold to buy a SinglePlayer scenario/achievment where you would have someone else play your account is much higher then to buy a RIO Rating or Curve.
So it makes it easier to find People with appropriate skill levels.