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Sure, you could rip them yourself (and I will, as lossless files to play on my main stereo), but that both takes a bit of time and you would then have to add the MP3s to your Cloud Player account. Instead, with AutoRip, Amazon puts the MP3s in your account as soon as the CD ships (for most CDs, you can start listening right away) and you can download them, the same as any other MP3 on your account), to put on your MP3 player or iPod.
There are a few conditions, of course. The program is limited to those in the US (presumably the only area where Amazon has negotiated rights to distribute the MP3 "companion versions" and if you return the CD and have already downloaded the MP3 files, they'll charge you for the MP3 version of the album (you still have the usual refund restrictions on the CD). If you haven't downloaded the MP3 files, then they simply remove them from your account if you return the CD. If you like to trade CDs at a local store or sell them off after a while, then the MP3s stay in your account, since that is outside of anything to do with Amazon.
I browsed thru the AutoRip eligible CDs at Amazon and noticed something rather interesting - they often display an import CD (at a very high price), but there will be a US version of the CD at a price much closer to the MP3 album and it will also be AutoRip eligible. For some of the albums I looked at, you paid only about 50 cents more for the physical CD (especially if you are a Prime member and get free shipping), but had all the immediate listening benefits of the MP3 purchase.