There are a lot of people who only consume a certain type of salt. More and more people are now consuming iodized salt as the salt that they add to their food at home. Salt it iodized because iodine is one of the nutrients that the body needs but does not get enough through the food that we eat.
The main reason why this was started in the first place is that of the disease goiter that was rampant in the past. Iodine is supposed to lessen the chances of getting goiter. It can also help heal other conditions that the body may be going through.
Table salt or iodized salt intended for human consumptions is typically first mined from underground salt deposits or evaporated from brine. Salt contains about 97 to 99% sodium chloride. After mining or evaporation the salt crystals are processed to eliminate minerals and rocks and an anti-caking agent is added to allow the salt to flow freely and to prevent clumping.
Most table salt also has added iodine, which comes from potassium iodide. Iodine is an essential nutrient that helps maintain a healthy thyroid. The same processes are used to make salt for melting snow and ice, but obviously the purity specifications are not as strict since people are not supposed to eat salt made to melt snow or ice.