The theory behind this is sound, and I’ve seen it in action: the young dog in the ring doesn’t really understand what’s going on or what his handler is asking of him, so he performs the only trick he remembers really well: sit. Oops. Failure to stand on examination can get your dog tossed out of the ring, or “excused.” I can see where this is a problem.
The substitute “stand” command is supposed to get your show dog to stand still. This should be sufficient in most situations to keep your dog from getting in trouble outside the ring if you just need him to freeze. I use it consistently with Kunga and he’s almost forgotten “sit” as a result. (My non-show Bloodhound has “sit” burned into her brain and does well with it generally.)
But I must admit, I miss “sit,” for a bunch of reasons. There are times in small spaces when it would be handy to have Kunga take up less space and be a bit more under control than seems possible with “stand.” Then there are all those times that I take him out in public–to the bank, the photo lab, the pet store–when it’s tedious to explain to well-intentioned people with treats that “sit” isn’t really in my dog’s vocabulary.
If I ever decide to try performance events like rally or obedience with Kunga, he’ll have to re-learn “sit.” But for now, he just stands, wagging his tail like mad.