Typical table salt has very small portions of Potassium-Iodide added to it (supposedly to prevent iodine deficiency disease of the thyroid gland) which some people (mostly those selling sea salt!
) claim is responsible for rampant hyperthyroidism.
The sea salt craze if fueled by the uber-health conscious folks out there but most of them are duped anyway. Most of what is sold as sea-salt is just as refined and processed as the table salt is.