You're talking out of both ends of your alimentary canal. It's more difficult, but it helps any pull?
Besides, this is the BB forum. All we're interested in here is how to make things bigger, and keeping the shoulders retracted doesn't seem to be as effective for rhomboid and trap size as moving through the ROM with an appreciable load.
Allowing the scaps to protract, and then forcefully retracting them against a load has nothing to do with humeral rotation, and it doesn't put you at risk for injury.