I respectfully disagree on both counts. Auto changes are highly desirable in hunters, jumpers and event horses. They are very much frowned on in dressage, for very good reason, but we established early in this thread that the poster is not interested in changes for dressage (she's not competing at that level) but for changes on course either eventing or show jumping.
And I haven't found it all that difficult to ask a horse with auto changes to delay a change or counter canter, it's merely a matter of maintaining the previous bend and preventing the change. Very common when a horse competes both in hunters and hunter seat equitation; the flat tests in the Big Eq classes include are changes on a straight line and a simple change for exactly that reason.
I suppose that if you trained them correctly it could be helpful. But I personally don't like it when a horse does something when I don't ask it. In my mind I see it the same thing as if I was walking and the horse would leg yield every time I went on the quarter line.