Thank you! Paul Maye is a good friend of ours, and a great instructor. A different carriage driver instructor taught me how to long line, and I use it as part of the training process for starting young horses and, in this case, to complement training for a pony that does dressage and jumps (doesn’t drive…yet ).
Yes, it’s wonderful for developing softness and stretch over the back and strengthening the topline.
It’s such a fantastic skill set to have in your tool box but it is so easy to do it wrong (been there, done that). As @Platoon mentioned, using it to demonstrate whatever needed to be demonstrated in this instance only created more pain and discomfort for the poor horse. Long lining should not be used as a way to “control” a strong horse, ever (which is the reason Amos provided for its use).