Although not essential it may replace some potassium as a plant nutrient.
Sodium is necessary for hydrochloric acid production in the stomach.
Sodium is absorbed in the upper small intestine, and enough sodium is retained to maintain blood levels. Daily 1 g sodium chloride per 1 kg of water consumed. Excess sodium in diet can cause potassium to be lost in the urine. Too much sodium can increase blood pressure. Some in skeleton but much more is in extracellular fluids.