They're useful for keeping track of cognate manuscripts, and I'm setting up one to do that for a manuscript collection I've been working with for some time. As an aside, you can't tell that from my recent publications, as I've just realized, so I'm wondering what I could quickly throw together as a note, just to put something out there with my name on it and keep marking my territory. Discussions of scoopage at Notorious's place have me slightly spooked.
But anyway: a cognate manuscript is one that shares texts with another. Since the collection I have in mind is a large one, I'm not interested in manuscripts that share only one text with this one (though if you had a smaller batch of texts, you might be). Two or more shared texts, however, and I'm paying attention. So here a spreadsheet is very helpful: it's easily searchable, and gives a clear visual representation of which texts appear in different cognate manuscripts.
I think I'd need a three-dimensional spreadsheet to do a perfect job, because ideally I'd want to show all the contents of the other manuscripts, to indicate what they have that my main interest doesn't. I can imagine this in some sort of holographic device, color-coded so that the shared texts would really stand out. But I'm not so technologically inclined as to be able to create the holograph-cube.
I'll just make a note of it for my sci-fi novel about manuscript study . . . .