With all the metadata available these days (IPTC, EXIF, XMP, OMGWTFBBQ), I do wonder what use some of them are.
Take the examples from Wikipedia's EXIF-article for instance. Sure, there are times where I can't live without the Interoperability Index and the compressed bits per pixel, but at those times I've usually been forcefed liquid stupid.
I'm sure there are scientists or something out there who actually use some of these obscure values, but to the overwhelming majority of almost everyone they don't matter!
So which ones do matter to you?