Answer : Kosher salt, like most supermarket sea salt, is much coarser-grained than ordinary table salt. That makes it take up more volume for the same amount of weight, so you may need to adjust the amount used if a recipe calls for regular salt; check the koshersalt box for a conversion factor. (Morton, for example, says to use the same amount of kosher salt as specified for table salt, except in recipes requiring more than a quarter-cup; then you should add an extra tablespoon of kosher salt for every quarter-cup.)
Kosher salt does not dissolve as quickly as table salt, making it useful for giving a salty feel to the exterior of foods without using as much salt. In fact, this property is actually the reason for the name kosher, because kosher salt can be used to draw the blood out of meat, as prescribed by Jewish law. Almost all salt, including table salt, is kosher certified. Unlike most table salt, kosher salt is not iodized and is commonly free of other additives as well. (Morton kosher salt, however, contains yellow prussiate of soda-sodium ferrocyanide-as an anti-caking agent.)
As for sodium content, if you substitute kosher salt one-for-one for table salt, you will slightly decrease your sodium intake because of kosher salts greater volume: One teaspoon contains 1,920 milligrams of sodium, compared to 2,325 milligrams in table salt. By weight, however, both kosher and table salt contain about 400 milligrams of sodium per gram.