Which process is preferred to separate salt from water, evaporation or distillation?
The answer to this question depends on whether one is trying to recover fresh water or salt as a result of the separation. Distillation is the separation of substances by boiling. The boiled liquid is condensed and collected. Evaporation is the change in state from liquid to gas at the ambient temperature. It's a slower process that distillation and usually makes it impractical to recover the evaporated liquid.
Evaporation is the preferred method of obtaining salt. Sodium chloride is produced commercially by evaporation of seawater in large basins. Energy is provided naturally by the sun, eliminating the cost of electricity or fuel that would be needed to harvest salt from seawater by distillation.
Distillation is used when the goal is to recover fresh water. Distillation plants located near oceans can produce large volumes of water when other fresh water sources can't meet the local demand. Electrical power is needed for distillation.