Field notes: Pencil, perspective and a poem bench
For the most part, I stay away from pencil --unless I'm doing a pencil sketch-- for several reasons. Inking previously drawn pencil outlines can diminish the feeling of freshness and spontaneity that makes sketches interesting. The added step of penciling before inking also makes the process longer. What I normally sketch in 20 or 25 minutes would take me 45 minutes to an hour, including coloring, if I penciled first.
But in some cases I use pencil to block out the main elements of a composition. Pencil comes in handy to mark the horizon line and vanishing points when you are drawing wide open spaces and want to get the perspective right. That was the case with the drawing of Gregory Harrop's poem bench, or with my lead sketch of the streetcar on this other story. In such cases, if the perspective isn't fairly accurate, the drawings start to fall apart.
I like to keep the lines light and not overdoing them, using a 2B pencil. Some sketchers erase them before inking --a kneaded eraser won't damage the paper--, but I mostly let the pencil marks be part of the final drawing. You may call that a "transparent" approach to sketching, where no tricks are hidden to the viewer's eye!
Sketching results by artists who use pencil before inking vary greatly. That's a good thing about sketching. Whatever method you use, your unique style will still come through. For example, just compare the work of Thomas Thorspecken with the work of Gérard Michel. Both start their sketches with some pencil outlines, yet their final results are completely different.
You can browse a gallery of sketches and purchase prints.