For people reading along here who may not build fence daily, a former boss of mine had a scar that went for a little under his eye almost down to the edge of his mouth from some one pulling barbed wire with a tractor when he was a kid. It parted and went flying. The wire cut clean through his cheek and almost got his eye. Did the tractor cause it, did the wire have a kink or bad spot? We dont know that part.
Its extremely easy when using machinery to over pull wire, especially a single wire. When you are controlling the pull with some thing like a come along, it's like having a fish on the line, you can feel it and and have a little more control. You have to really get down on a hand crank to break it. Kind of like using an air impact vs a hand ratchet.
You may pull wire 100 times with your tractor, it may break 5 of those and fall to the ground, but it only takes that 1 time to go across your kids face and you will spend the rest of your life wondering if you shouldn't have just done it by hand.
I watched chains bust and fall dozens of times winching up equipment on trucks in my life before one time I saw it slingshot right into his back headache rack. I took the stand back call a lot more serious after.
How many times have you seen a rope break when guys are roping? A friend of mine who does it for a living had a rope bust when they were dragging a cow up in a trailer with a tractor. He was pointing in the air to the guy on the tractor to go ahead and the rope snapped and whipped around and chopped his pointed finger off a foot or less from his face. It happend so fast he didnt realise it at first. Would that have happened with a horse dragging?
Just consider the risk vs reward before you do some of these things. Short term gain does not always pay off long term.