in my current understanding & personal experience, 1 significant advantage of
moist sea salt is its mineral contents as well as the presence of (most) volatile elements in fresh ocean salt
mine salt -- real salt, himalaya, etc. -- on the other hand, no matter how pretty it looks, is an old thing, buried for ages while losing its potency
sea salt from northern france, celtic & similar brands, is collected in an ever cloudy area & dried mainly by the constant wind there (not overdried by sun or heaters); its moistness reflects its high magnesium content
as far as how to use salt, this is my own personal experience:
in the past i had problems with no salt whatsoever as well as with sprinkling salt grains directly on my food
so this is what i do now: prepare a brine with moist sea salt, which i keep in a glass jar in the dark & cool & then dispense with a dropper into my drinking water or (fresh or fermenting) food
in my mind, this using a brine instead of dry salt makes a lot of sense: salt comes from the ocean, within which it's constantly dissolved; that's how fish & algae use it
re. where to find it:
celtic salt is available at whole foods; another french brand is found here (1 or 5 lb i.e. 1/2 kilo or more bags):
http://www.saltworks.us/shop/product.asp?idProduct=264
