One customer, a rather small-ish woman with a rather huge Bloodhound, tells me that her 15' Supergrip line makes a big, big difference in her ability to hang onto her hound as he attempts to drag her along.
Schutzhund folks use Supergrip for agitation leashes because, when the dog lunges, you can still hang on. That's important. The helpers tend think so too.
Most recently, I have had clients in other dog sports (nose work comes to mind) who like fact that the super grip allows them to continue to participate in these sports long after their arthritic hands might otherwise have forced them to retire from the ring.
Supergrip is not for every situation or for every dog and handler. Before you buy it, I feel that there are 2 issues to consider:
Weight - It is heavier than the normal Biothane. Because of that, I do not recommend it for lines over 15' (personal preference).
Grip - It has such great grip that it does not slide over, under, or around trees, posts, rocks and other items along your path. This is not a problem in a short lead, but it can be an issue in a longer line, especially outdoors in congested areas or woods and scrub.