I have never seen the benefit. Most of those who talk about it end up one-side weighted and on the floor, or easily blocked and blown through...dang...there's that martial talk again!
The use of the shoulder is going to isolate the arm from a clean path of power through the body.
There are other more sophisticated things you can do in generating power in the hand from the hara/ground...say in one direction, while the elbow can generate a different force in an entirely different direction... and so on. There are various ways the hand itself can express power from different parts of the body. Some of that joins IP to IS and aiki.
None of that is going to work when the arm/shoulder is in isolation.
Okay, I can accept that to some degree. But what would qualify as isolation? Like, someone throwing a punch with mostly muscles around the shoulder joint being used, and the rest of their body just mostly bracing? Or does even extending the whole body, if one is careful to simultaneously activate every muscle in the chain, including the shoulder, count as isolation here, so long as the shoulder muscles are working at all, even if in concert with the entire body?