Some people I know like to use a 'grazing' curb on trails. Which basically means a curb with no joints for grass to get stuck in.
That's not a good enough reason, for me though, and there are a number of other things you can do, if you're going on long trail rides, where you want to stop and let your horse graze. I'm not a fan of letting the horse graze while you're on them, because I believe it teaches them to try to graze other times, when you're wanting to work.
I'll only let a horse graze on trail, if I'm off. So in that case, if the horse is hobble train, you can stick some hobbles on and remove the bridle completely.
Or, they make trail bridles, where you can easily take the bit off and it's basically a halter.