There is a commercial market for salt -- and for stuff like treating roads in the winter it doesn't have to be very clean.
Otherwise, disolve it into the local waste water stream and discharge it back into the ocean.
Either it's not as big of deal as people suggest, you are wildly underplaying it, or somewhere in between. I've never felt that the argument against being the cost to heat the water was a strong one since salt water pretty much means a coastline which tends to have steady wind and sun. The biggest hang up has typically been putting that brine back into the ocean.