Like DeerAssassin says it will leave a pair of underwear funny colored. I dropped a small trailer while doing about 50 (I forgot to lock the hitch onto the ball) only had about 300 lbs of junk on there and since the safety chains were hooked up I got a nice dent in my bumper and a bent trailer jack. The dent is a good reminder every time I hook up a trailer now to check it a 3rd or 4th time
Not loading the trailer with enough tounge weight allows the trailer to "untrack" I think is the correct term.
I haul tractors on occasion. I have to be real carefull about where the tractor is positioned on the trailer, and if it has implements attached or not.