Teresa:
Adding salt to water in livewells (& shipping containers - ???) for storage/transport of caught fish is widely practiced. It reduces stress on the fish - see
Angling Mortality (especially Bob Lusk's great post down a little ways) and
Baffling a Shipping Container for recent info on this. Salt water dips for wild fish being stocked into ponds is also recommended (by Bill Cody, at least - a "foremost authority") to reduce the incidence of disease and/or parasite introduction via the new fish. I don't think anyone has posted on actually adding salt to their pond here, though.
In the first link above, Burgermeister
asked about adding salt to an entire pond. Bob Lusk states adding salt to ponds is not necessary because the fish there aren't being subjected to the stress of transport/handling (that's plenty definitive for me).
Now, Bruce Condello has fairly high salinity in his ponds, due to fairly low rainfall/watershed size and fairly high evaporation - resulting in very low flow-through of water. Bruce has commented on this as (possibly) being beneficial for his fish at least a couple of times. Hopefully we can call upon him to expound on this thought here.
Yes, Bruce, I'm setting you up against The Great Pond Boss himself. :p