I hate long billets. Nothing like having to choose between tightening your girth and risking your life on a fractious horse. And, um, this was on a horse who’s normally a rock, but it was cold, he’d been in all night, and we were at a competition. If my D saddle weren’t completely wonderful otherwise, I’d never tolerate it.
I also don’t like them from the horse’s perspective: too many edges against the horse, between the edges of the billets and the edges of the girth, however well padded. I’ve never had a problem with the buckles of a long girth under my leg that I couldn’t solve with a girth a couple of inches longer or shorter, so that doesn’t affect my preference.