It is not all that unusual, especially for trainers with too many horses and too little time or good assistants. It will teach a stiff, resistant horse to 'follow its nose' , but I personally think there are better ways.
Even more trainers tie a side rein to a girth or surcingle. I would think this trainer is much more moderate (if that is the right word) if he tied the lead from the halter noseband rather than a rein attached to the bit.
The one positive thing it does that tying a side rein to a girth or surcingle does not do is it encourages the horse to bend its whole body as opposed to just bending and giving its head and neck.
I have seen unattended horses flip over if they fought this hard enough. There are better ways.
I like taking a long lead-rope and bringing it behind a horses rump and pulling the horse around to 'un-wrap' itself. It works very well to teach a horse to follow its nose and you can put as much pressure or release it as you do it.