Metadata – Which ones are important?

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?

In my images, that would be the © data. In yours, it would depend on how you screwed the image up?

Thanks for the enlightening comment PhotosGuy. I'm looking for more than one opinion/personal preference/experience though.

One has to realize that the all the fields in the metadata files are there to cover a number of different industries. If you are using photoshop it is possible to control which fields will be shown. I certainty don't employ any of the obscure fields. I have presets in a number of different applications that will populate all of my personal information. Beyond that I use keywords on virtually every image I keep and on some will go further and title an image and provide a description. It's simply a matter of personal preference as to which ones you want to use. It is time consuming to keyword all shots but time that I feel is worth the effort.

I do keep the metadata when I export an image from Lightroom because for one reason I like having the shooting info in the exif -- it shows up in the display in my Web host (Pbase) and, when I'm sharing images here it can be helpful for people to check out the data.

Keywords can be very useful for checking for a certain, well, keyword, whether in LR or Bridge or, for exported jpegs, any number of keyword-aware programs.

Other than those things I don't mess with metadata, although I do know that in, say, Bridge I can check out the work I have done on a jpeg image in Lightroom/Photoshop -- I guess that could potentially come in handy if I lost the Lightroom metadata and wanted to "reverse-engineer" the work done from a jpeg...

I believe the ICC section is what certain web browsers use to determine the color space that the image is in. I've recently decided to keep that section rather than completely stripping out all EXIF for images that I post online.

I don't get why anyone would strip exif info at all, actually.