I was taught to do auto releases by a connemara pony who used his amazing athletic talent for evil instead of good
I swear he could change his mind about doing a fence when his front feet were already off the ground! He was a master of the refusal and would also bolt or change direction suddenly... He could do a 90 degree turn in the middle of a one stride combination. With an auto release your weight stays centered over the saddle so if something unusual happens you are less likely to fall off. That's probably why you see more in x-country where anything can happen. My teacher was not an auto fan and used to give me hell for it, but I was the ONLY one who never fell off that pony!