Show leases are slip leashes, and also know as 'the garrotte'. They are positioned high up on the neck to give maximum control (same case with some other collars,like the prong). As they are just a thin rope, they can definitely hurt a dog and are not recommended for use in regular heel training. And to me, it looks like the dogs hold their dog in a slightly unnatural position due to the leash (neck held higher than it would be normally). But, that is the position that is desirable in the ring, I would guess, as it makes the neck and head so visible.
And ring handlers obviously know how to train with this leash.
There was a documentary made about negative (in some cases tragic) changes that breeders were making to dogs (posted here at some point). One was increasing the slope on the GSD. In some cases, the change was so extreme that the poor dogs couldn't want or run properly and medical issues resulted.
Not a good watch before watching Westminster, obviously.