You do have to be careful with a grazing rein though. I use them on all my lesson horses, because we work in a grass ring with little kids. The one horse I own (not a lesson horse), that I don't use it on, it's because he panics, even if it's not really tight, because there isn't any give once they get to a point, and it freaks him out. He starts slinging his head and trying to rear. (Luckily, he doesn't need one, so it isn't an issue.) They are wonderful things, but never use one unless you've tested it out from the ground first.
"Keep a leg on each side and your mind in the middle"