I’ve had a couple of horses over the years who were absolutely night and day in the differences in their hind end “engine” with and without hind shoes. And with those horses I had done shoes up front (only) for the first few months and then added hinds when we got ready to head to a show where I would need to caulk them. Adding shoes increased the power and drive from behind significantly. So now when my young horses get to the shoeing stage, I put shoes on all 4 feet (rather than my former plan of shoeing up front first and following with hinds 6-12 months later).
I’ve also had horses that felt no different when hinds were added - so I don’t think it always makes a huge difference. But I’m not interested in taking my chances on which type of horse I’m sitting on, and eventually shoes will go on all around anyway.
I do have one mare who’s in fronts only. She’s 21 years old and packs around my 9 year old daughter. So I’m not terribly concerned with her ability to drive from behind (though I do think she goes better when she’s shod all the way around). But also, she’s my alpha mare in my herd of mares, and is the one who does the most (if not all of the) kicking in the pasture. So after she nailed one of my young horses in the shoulder years ago, she lost hind shoe privileges!