You mean holding them like you would driving reins?
Yeah, I've been made to do that before. It was to stop me from picking at the horse (making constant small adjustments) on the way to fences. It either works because you don't have those little fingers on the reins to wiggle, or just because it's "different" and your brain is working out how to deal with it instead of doing what you were doing before out of habit.
And if THAT doesn't work, the next thing is to unbuckle the reins and cross them *under* the horse's neck!
It is called the Fillis method of holding the riens. It is supposed to keep you from pulling down on the horses mouth. I have never tried it but did see it offered at a clinic and wondered so looked it up.
It's been used for stiff hands, locked elbows, auto release as mentioned. Teaches a rider to bring their arm back to their body connection. You can't pull back with your hands only, you need to use your shoulders back down to your seat.
Neat trick with the rein cross too. Too many people ride off their hands, have to use something to make a different muscle/brain memory. I use a lot of wheelbarrow reins and carry the hands exercises also to get a rider to sit up, back and down and use their seat and help create independent soft relaxed hands.
... Reminds me of my safari in Africa. Somebody forgot the corkscrew and for several days we had to live on nothing but food and water. W. C. Fields
Been having some of my students riding that way recently. It teaches feel and a following hand. It seems to align the body in balance with the horse. It teaches the automatic release and the concept of the hand belonging to the horse. Finally, it prevents the two forearm bones from locking, allowing for a flow of energy from horse to rider.
Anne Kursinski has used that hand in her clinics, and my trainer of 55 years ago encouraged it!
Form follows function, or does function follow form?