[Delirium-Zer0]

It came into use for two main purposes. One was the importing of western cds, so that the cds could be alphabetized by their katakana spelling. On domestic (japanese) cds, it was used to advertise the artist's other releases (you still see that sometimes on japanese cds now). Now a japanese cd just looks bare without one, so they're almost always there, just for decoration really. Alot of times the designer of the artwork will use it for the track list, and with some CDs, you NEED it if you want to keep the tracklist (i.e. kanariya, Fly high... it's hard to read the one inside Far away so having the obi helps). It doesn't help make it easier to see what cds are real, as the few japanese-manufactured bootlegs i've seen also include obis, and HK/China manufactured bootlegs don't end up in japanese stores, as that'd be too damaging to the japanese economy. Japanese CDs are expensive, and japanese people know that. Western CDs almost always have to have extra bonus tracks and have to be released up to a week in advance of their original street date just so they're a little more appealing to the japanese people than their western counterparts. But i digress.

Oh, another thing is (again, a design thing) that the release date, price, copyright info, and UPC scan code are on the obi, so as not to interfere with the design of the back cover. (Just compare the US and japan versions of Utada's Exodus there. The US version is just ... yuck >)