once you get past 'processed' salt, they are ALL a little different - the sea salts from different places and the mineral salts too.
They are varying levels of the various elements that are in them, including or not including iodine and others.
Not only that but they also TASTE very different as anyone who has cooked with them will tell you.
For example, I just used a Trapani salt in a little burlap bag which was truly the most salty and delicious I ever used - much more than the French ones. The crystals were huge and as clear as crystal (not that white look).
This is not something you need to be an expert on to taste the difference, it will knock you over the head!
If a person has a less than superb thyroid or a water retaining tendency, or any other sensitivity to salt then these differences can be very noticeable.