There is nothing more beautiful to a motorcycle junkie than a brand new chain covered in the thick layer of grease, but that lube will not last more than a couple of hundred miles. Chain lube is a necessity if you want your chain to last more than about 10,000 miles. The problem is that most of us would rather be out riding in our favorite twisty roads than rolling around on the garage floor with our hands covered in grease.

Modern motorcycle chains have internal lube that was put there by the manufacturer and is held inside by O-rings or X-rings. This lube greatly reduces wear between the pin and bushing of each link, but there are many more parts that have metal to metal contact like between the roller and the bushing the roller and sprockets. These parts need lube to slow the wear and the O-rings need lube to prevent drying out and cracking, resulting in loss of internal lube.  

Wear manifests itself in elongation of the entire chain as each link wears a little. Most modern chain manufacturers recommend replacement at 1% elongation from the original length.