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They are an online spice store. Its pretty simple but there are a few reasons I really like buying spices online.
1) Their spices are likely to be quite a bit fresher than any grocery store and possibly fresher than boutique spice stores, because of volume. They ship and process more spices and have less sitting on the shelf for who knows how long. However as spenzys points out, some spices like pepper are only harvested once a year, so no need to throwout your spices more frequently than that.
2) Price. You can purchase spices in glass jars, or in plastic baggies and they are quite inexpensive. Once you have a spice collection and the jars for it, you can buy their inexpensive baggies for refilling.
I would also imagine their quality is better than the average supermarket spice. But I am not too picky.
Some gratuitous pictures:


You can see the bags of spices in this pic:
Anyway I just thought you guys might be interested, I am sure many of you already order spices online.
P.S. Sign up for their catalog, its beautiful and has some amazing recipes.