Interesting discussion so far. I'm riding english and I ride on trail "on line". :) I mean I don't keep full contact like I do in ring, but I still keep some. Two reasons for that
1) My paint is spooky. I mean, I trail ride her for 3 years already, still ANY new thing (like new bridge, or fallen tree) makes her very unsure and takes us time to cross. I've never seen a horse that would be SO careful about where she goes and steps she makes (and I tried lots of new trail horses for the sell barn). I don't pull on her mouth, but I rather prefer to keep the reins short if she decides to jump over the obstacle (that happened before, VERY big jump from stand still) or shy on side.
2) If I give a loose rein to my qh she drops all her weight on front and nose goes almost into the ground. With some contact I remind her to keep her head higher and work from her hind.