> Does paper have any advantage over vellum ("sheep skin") other than being cheaper?
Ink takes far less time to dry on paper as opposed to vellum from my understanding. It's also thinner and easier to use in printing presses. Paper also can be produced in various thicknesses/with various textures to allow for different kind of work. (Think newspaper paper vs. watercolor paper). Paper is also recyclable - you can break down paper and use it to create new paper.
> Paper also can be produced in various thicknesses/with various textures to allow for different kind of work. (Think newspaper paper vs. watercolor paper
Again, this sounds like it's purely driven by cost concerns. Newspapers aren't printed on paper that's better suited to being a newspaper than the normal stuff. They're printed on awful, kleenex-like paper that will tear in a light breeze and that smudges ink all over you if you touch it at all. But I assume newspaper paper is even cheaper than other paper.
(And indeed, newspapers with a high opinion of themselves produce separate "archival quality" editions on non-awful paper!)
Clay and vellum can also easily be produced in "various thicknesses" (see: palimpsests!), though admittedly it's tough to get clay to be as thin as you'd like.
Reusable =/= recyclable. Palimpest is more like erasing pencil writing and then re-writing.
> Again, this sounds like it's purely driven by cost concerns.
It's not - I was thinking of fine art applications. You can't make tracing clay or vellum, for example. Or textured paper to work with different types of paints/inks.
Ink takes far less time to dry on paper as opposed to vellum from my understanding. It's also thinner and easier to use in printing presses. Paper also can be produced in various thicknesses/with various textures to allow for different kind of work. (Think newspaper paper vs. watercolor paper). Paper is also recyclable - you can break down paper and use it to create new paper.