Well, there are many advantages - coatings provide protection from fingerprints, atmospheric pollutants, UV light, moisture, and help provide resistance to scuff marks on prints made with pigment inks. Further, Wilhelm Imaging, the only real authorities on the issue, indicate that coatings can seriously increase the longevity of your prints (especially a concern with dye based inkjet printers).
Another reason to coat prints is to reduce bronzing and gloss differential - in most cases, coating your prints will eliminate all but the most severe problems.
We currently only have one product to choose from. This product is one of the only endorsed by Epson and HP for coating inkjet prints:
Premier Art PrintShield - independently tested by Wilhelm Imaging and universally held in the highest regard, this is the classic inkjet print coating, suitable for all papers/canvases, except super high gloss papers.