Pifft! Preliminary Sketches!
It's rare I work from sketches mainly because the sketch is part of the work. I usually start on a panel and work out all my ideas there. "Preliminary Sketches" are the being of the work so to leave them out is like throwing away the bones.
For illustrators "Preliminary Sketches" are were you work out your mistakes. I am not an illustrator. Every mark I make is an important part of the final work. Sometimes a mark is there from the begin of the work and becomes a pivotal part of the painting. The evidence of the mark is exemplified with the constant rebuilding of the original mark. How many times have you made a sketch of an idea only to realize you like the sketch more then the final work? That is because the spontaneity is worked out of the piece. The first marks are important, they record the raw emotion that caused you to record the idea in the first place. Even if the original marks are scraped out the evidence of your erassing the marks are still there.
see: Robert Rauschenberg's "Erased Dekooning" 1953
drawing | traces of drawing media on paper with label and gilded frame
For illustrators "Preliminary Sketches" are were you work out your mistakes. I am not an illustrator. Every mark I make is an important part of the final work. Sometimes a mark is there from the begin of the work and becomes a pivotal part of the painting. The evidence of the mark is exemplified with the constant rebuilding of the original mark. How many times have you made a sketch of an idea only to realize you like the sketch more then the final work? That is because the spontaneity is worked out of the piece. The first marks are important, they record the raw emotion that caused you to record the idea in the first place. Even if the original marks are scraped out the evidence of your erassing the marks are still there.
see: Robert Rauschenberg's "Erased Dekooning" 1953
drawing | traces of drawing media on paper with label and gilded frame