These days, most of our models are wearing cock rings simply for cross promotion of the Xtreme cock rings we produce. If we are shooting Raw Studio gear, then it's to cross promote all the cock rings Raw Studio produces.
In the past (we've been at this for 17+ years) we would make a judgement call based on how the pouch looked. If the model had less of an endowment and was modeling a jock with a generous pouch, getting the model to wear a cock ring would often make the pouch a bit fuller. It was never to get the model hard or even with a semi, worn loose it would be enough to reshape the pouch.
Another issue is with guys like Evan or Matty who have big hefty cocks and big hefty balls - with them, some pouch will end up flat simply thanks to gravity. So wearing a cock ring for them will give everything a bit of a lift.
In the case of Chance and the Pro Jocks, Chance has huge balls and really didn't need help filling the pouch, it was purely for cross promotion.
We've always joked around here that it's not the dick that fills the pouch, it's the balls. I guess there's a bit of truth to that.
I guess, there's also been times we've simply asked a model to wear a cock ring for the fun/thrill of watching them play around with their dicks trying to get a cock ring on!