St5 ignores header data. So if your workstation changes header info, like samplitude does, an st5 of the raw wav is a good idea cos u can always check the files after a while if you decide to go back and remaster, u know u are working with the same exact wav file u originally recorded. An st5 is also good when checking files transferred from hd to hd, since an md5 of the original transfer/save is useless if the header data changes due to the way your wav editor works (found the latter out the hard way)...
Furthermore, when mastering to redbook, since st5 hashes wav data, you can st5 your final wav tracks, and compare to the ffp from the final flac files, and know your encode went flawlessly prior to seeding. Simarly, when Joe Downloader makes his CDs, he can make his own st5 (or use the one I include in the seeded fileset); if it matches the downloaded ffp, then the flac > wav conversion went right, and the files are ready to be burned to standard.
Ymmv