Why does the body crave salt?

"The amount of sodium chloride in human blood and in urine is always kept within a very narrow range of 9 g per L (0.9% by weight). Drinking seawater (which contains about 3.5% ions of dissolved sodium chloride) temporarily increases the concentration of sodium chloride in the blood, so the only way to excrete the excess sodium chloride in the urine is by sacrificing internal water from cells. The cells eventually give so much water to try to dilute the salt that they die from dehydration, quickly followed by organs and eventually the organism."