My expectation has always been that if I loaded a book back onto the device after stripping the DRM, it would appear as a different book to the Kindle than the original. I doubt that highlighting and page synchronization will work.

So, yes, the main purpose of DRM stripping -- at least for me -- is as part of backing the books up into my Calibre collection. I don't bother to copy the stripped copies back onto my Kindle, there's just not any compelling reason to.