A sketch is like one of many fibers in that fancy dress you wore out to dinner last week. It's that little bubble of creativity not quite large enough to pop; the tiny glow of a lightbulb that hasn't gone off yet. It's the little thing that most writers often talk about "floating around in their head"- so yeah, they weren't kidding.
A sketch is an idea that could exist [flimsily] on its own- leaving the reader to interpret the rest of the scenario. Like a page torn out from a mystery novel, that you find on the floor of the library. Or it could be that one ugly bead you tie the string on when you make a bracelet to keep the other beads from slipping off- something small that helps you create something bigger.
I used to throw away my sketches. I thought they were useless, dead-end ideas. It's only recently that I've realized they're special in their own way. They may not be complete, but they do tell a story. They tell you [almost] everything you need to know about the 'what.' It's your job to figure out 'why.'
