There's no difference. Except that the processing and shipping of ions is passive / much easier. Contrasted with large permeable membrane plants that have to burn power to push all that brine out into the ocean.
Seriously though, far out to sea away from any landmass it's pretty much a desert. Any salt dumped there would disperse very quickly and not pose a problem to wildlife.
Almost every part of the world ocean has been described as a desert, before people went under and looked. It turns out there's a huge amount of life everywhere you look, even miles down.
But there is also a lot of room, so anything localized, unpleasant, and temporary can be swum away from.