At least half of all NaCl that's used world wide is mined from salt mines. For many places in the world it's not feasible to rely on solar evaporation of sea water. Using other energy sources to evaporate sea salt is not cost effective and many places have large salt deposits.
desalination wastewater contains a number of other chemicals used in the desalination process (e.g. pH adjusters, coagulants and flocculants, antiscalants, dispersants, biocides, and reducing chemicals)
