[SIZE=12pt]You bet
My story involves not a nylon harness, but a VERY thick & cheap leather harness. When Mia was 2, she and I were driving her little gelding Teddy. Teddy was a very experienced CDE horse with literally thousands of miles in harness. He was super sweet and steady as he could be. [/SIZE]
Mia and I were driving around a large square drive around our neigbor's property at a good road trot when Teddy suddenly went airborne and bolted. This wasn't a spook or a canter, he was flat out and twisting & , bucking as hard as he could. When I tried to pull him around to circle, the cart flipped. Mia was thrown out, thank God. I'm tearing up and shaking just remembering watching her fly out of the cart. As the cart rolled, my left leg was trapped underneath and Teddy dragged the cart and me about 50' before I could wrestle his head around enough to get him stopped. I pushed myself away from the sideways cart, tring to free myself and he was leaping forward panicking, dragging me each time. I was on my belly, but free of the cart, still trying to hold onto him when he got enough momentum going to drag me again and I had to turn him loose.
I crawled to Mia (since I couldn't walk with a shattered lower leg), who was on her feet crying and scooped her up and looked for injuries. She was FINE, by the grace of God. It took about 10 minutes for one of the drivers going by on the highway to realize that I wasn't just waving, I was flagging them down for help. The wonderful lady called 911 and got first responders there, then an ambulance.
By the time Teddy was found more than 2 hours later, he had himself wedged into one of our large dog kennels, the cart still attached and on it's side, one shaft between his legs. Luckily he had only bruising and scrapes from bouncing off of trees & fences in his panic stricken run home. Who knows what all happened between where the accident happened and where he was found.
If we had had a good quality harness, I do believe he would have been able to break free of the cart during one of his many apparent collisions with things along the way. If my leg or body had been trapped in that harness (or a nylon harness), I would have been killed, there is no question in my mind about it.
We were SO lucky. Mia ended up with one tiny bruise on her forehead. When I had a chance to look at my leg, my foot was turned at a 45 degree angle to my lower leg. I ended up with all joints in my left ankle completely ripped apart and a shattered/crushed heel and mid-foot, where it had been dragged under the cart. I still walk with a limp much of the time.
None of this could have been prevented with a different harness of course, but poor Teddy would probably have at least been able to get away from the cart. If Mia or I had been tangled in the harness.... I can't even think of that:::::Shudder:::
The point is, we ALL want to stay safe and keep our horses safe. In a nylon harness, you have next to NO chance that it will break in an emergency. With a leather harness, you have a CHANCE, and some chance is better than none...