Question about "Sketch Sales"

What exactly do people do with the sketches, like what are they used for and all that? If I were to draw something up I could just upload a picture of it and sell it? (Being if it's good enough to be sellable lol)

You can line them and then use them for a sale or custom art. 

I'd say it depends on what the original owner says in the sale description. You can always use a sketch to make a drawing using the sketch as a base, but you just should make sure the original creator is okay with you selling the art based on it before you buy it.