I think the primary reason for a slightly descending strike on any full shot (besides driver) is to guarantee you hit the club face properly.
So, I don't think there's any real benefit to the shot beyond that. Think of the X and Y axis of movement through the ball - X axis is the lateral movement of the club through the hitting zone, Y is the "altitude" or the up/down movement. On a full shot there is so much friction between the face caused by speed on the X axis + loft that movement on the Y is not super relevant as long as you're hitting center face. If you were somehow moving upward at impact, like hitting an iron off a tee and jumping out of it, you'd expect reduced backspin - but I think you would not notice this if you hit center face. It's when you hit it thin that you see backspin reduced.
On short greenside shots, I believe there is an opportunity to add spin with a steeper hit. Since there is less X axis speed, you can manipulate spin with Y axis speed. This is also where sharp, clean grooves make a difference. There is not so much friction to overcome what you're doing at impact. Steep, clean strikes will bite more than a "sweeping" clean strike of the same loft.