Sometimes, after I've finished a story or a screenplay, I wonder if it might not be better served in another format. For example, I have a couple of screenplays that I'm probably going to rework because even though I liked the stories in their current incarnation, I feel they'd work better as novels.
I've also taken two short novels - Death Sword and Exterminating Angel - and adapted them as screenplays, even though they've been published. So why adapt? Because I want my stories to do double duty. I have published short stories I plan to turn into screenplays as well. Not all of them, but ones I think are suited to the cinematic format.
Of course, this brings up the question of which is better, the movie or the book? Since I'm only writing spec scripts, I can't answer that question. What I can say, though, is there's a reason why adaptations may deviate from the original source. I've even had to make changes. (While I was writing the screenplays, I found myself asking why I hadn't originally written the story that way. Oh, well, hindsight and all that.)
One reason for changing a story is that screenplays are meant for the screen. Many novels feature detailed descriptions and while this is fine, the writer will not be choosing the film's settings, unless he or she is also directing the film, such as for an independent project. Selecting locations is the production designer's job, in collaboration with the director and producer. So going into vivid detail about that Queen Anne Revival is fine for a book, but the production designer, director, and producer may decide that a Romanesque Revival is better suited for the movie.
Length is another factor, although in my case not so much. Most screenplays run 80-120 pages, and think how long some novels are, many with multiple subplots. Obviously, one keeps the main plot but with time constraints, it's possible that not every single scene of the story can be used. I ended up combining some scenes, not because of length issues, but simply because the screenplay flowed better.
Will anything happen with these screenplays? Hard to tell. But that's another post.