To me, the bit is where horse and rider unite, and the connection is influenced by the rider's whole body in the saddle. When the rider picks up the reins, the contact is the medium of communication. It can be harsh and strong, or elastic and light, or harsh and light, or elastic and strong. There are lots of riders who, whether by education or experience, aren't comfortable with the idea of contact, but for me there is no dressage without it.
Anyway, my young horses both have very busy mouths and so I have often wondered if they might prefer something different from my standard choice. There are thousands of different bits, so where do we start?
Here is a video with master horseman Bernie Traurig, that I found very helpful. Bernie is one of those rare creatures who has competed at the Grand Prix level of both dressage and show jumping.
Right now, Ehren is trying a french link snaffle wrapped in sealtex rubber and I'm finding a better contact at times with it, compared to the plain metal. Ludi will try it, too, and also a fulmer, which is known for being very stable in the mouth. We'll settle on their choice in the next month or so, and move on.
The old masters say "Set your tack perfectly, and forget about it.".... right after a bit of experimentation.