I always keep my originals. I did a large batch conversion from .mobi to .epub back in the day and there were some formatting issues on quite a few of the converted books. Always nice to have the originals on hand in case something goes wrong, especially considering the miniscule file size

You don’t need the original anymore. Majority of the original are just encrypted (DRMed) .awz, .pdf or whatever the publisher gave to Amazon. After you’ve done dedrm you should have the same content as original files. Storing all those working files just fill up your disks. Now there’s a potential loss in quality if Amazon or other online distributor do some type of optimization to the original files they received, which they do for a lot of manga, but there’s nothing you can do about that one besides not buying it from that reseller again.

Keep the originals just in case

I have an archive of all Amaon content, with the Kindle key as part of the atchive file name, so if there is ever an issue with my transcribed ePub files I ca scrape up the azw and crack it again.

Since Amazon stopped letting me download content, driving me off their service and to AA for the remainder of my digital library not offered by a DRM-Free publisher (Lookit you, Baen, still selling me stuff) or direct from the author, they also shut down access to the first generation Kindle devices (Which had more features that high end ones, now) so I’ll never need to update the cracks as I will never give Amazon another single solitary cent.