I've always found this an interesting aspect of publishing -- authors who get together, or are thrown together, between two covers.
These are obviously symbiotic relationships. (Symbiosis is a kind of mutual parasitism, which isn't a had thing in terms of species survival. Or writer advancement. In fact, it's a very good thing, since benefits flow both ways.) But what kind of symbiosis is going on in Authorland? Is it crass, creative, or convivial? Or all three? Or something else entirely?
A crass motive -- or maybe I should call it "pragmatic," which is less perjorative -- would involve an author seeking to enlarge his own footprint via another author's established fame, growing fame, industry connections, marketing savvy, fanbase segment -- you know, the aspects of the business that put a shine on reputations and money in the bank. Creative motivation is fairly self-explanatory. The parties are driven by a desire to stretch their wings, take some imaginative chances, and perhaps learn from each other. Conviviality as a basis for partnership simply means two writers genuinely like each other and think they'd have fun working together, maybe to alleviate the essential loneliness of this profession.
Just an aside: I wonder what brought Stephen King and Peter Straub under the same covers? Does anyone else have the feeling they probably did better as singles than as a couple?
So here are my questions. Why do you think writers hook up? And unhook? Have you ever seen evidence of unhappy or even disastrous pairings? Do you prefer to read collaborations or anthologies? Have you ever been able to untangle the authors' voices if the book is a collaboration (say, the voice of Vivien Dean from the voice of Pepper Espinoza in a Jamie Craig story)?
Feel free to throw in any other observations. I am, as usual, curious.