As important it is to shift the center of mass away from the front legs to prevent injuries as important it is to allow the horse a good stretch over the topline into a forward down as well.
For me, a proper forward down is when the horse is really searching towards the hand/line with a long neck, with his nose closer to the vertical so the poll/ears are going forward and down, and the hind legs are reaching far under his body.
From the ground we can see and feel it in our hand(s) because if the horse is not in balance, it will not look pretty nor does it feel light.
If done with essence, it is healthy and in my opinion a must to integrate it into the training so the muscles and topline can develop properly. The horses are much happier and more willing if they can relax, stretch and breathe in between hard work.