I heard the idea of rhythm beads is so you and your horse can listen to an established rhythm. The horse finds comfort in the steady sound, and you can easily regain a proper rhythm if something would happen to knock you out of it. Since you know what the proper rhythm "sounds" like for your horse and everything.
Theres also a theory that the horse will focus more on the jingle than they will on other sounds, so it might not spook as often.
A friend made my last horse a set of rhythm beads and they hung on my wall for a couple years. I never used them though I wanted to since he was the nervous type and its supposed to be a soothing sound.
I don't think I'd use them as a training advice. If I'm ever in a parade, they'd be fun to have.
And those who were seen dancing were thought to be insane by those who could not hear the music