Probably not, I'd say. I'm hopeful that the DNG spec will be amended so that JPEG originals can be stored as JPEG data, rather than as TIFF data. This would make the files much smaller.
About the onl reason I would suggest doing this is beuase you want to make parametric edits and send them off to other programs or users, and you want the recipient to have access to both the original and the adjusted image.
The downside to doing this with JPEGs is shown in this movie:http://www.dpbestflow.org/image-editing/parametric-image-editing#not