Different types of sketching
These are not technical definitions of the different types of sketching, but rather my interpretation and understanding.
1.) A sketch can be drawn to layout a drawing. The purpose of this sketch is to capture the main idea of a drawings. I use this type of sketch as a checkpoint to make sure the idea or message that I have in mind will actually play out on paper. If there is something I realize I do not like about my drawing, it is much harder to go back and erase when I have shaded in detail. But with a light sketch, things are much easier to change and move around. For me, this sketch is essential to creating large, beautiful pieces of art.
2.) Sketching can also be a collection of short and fast drawings. This can include observation drawings, figure drawings, or general small drawings and thumbnails. What differentiates this case from what I mentioned before is that a layout for a drawing is incomplete. Its purpose is to lead to something more. But when I refer to my sketches in my sketchbook, those are not sketches that I plan to add onto and make into more complex pieces of art. Rather, they are fast snippets of drawings that are complete. What I think decides if a piece is complete or not is the intention of the artist.
In the end, I consider sketches to be rough, quick, and capturing a main idea. This is what differentiates sketches from drawings or doodles. Drawings are much more detailed and thorough, not rough or quick. Doodles are simply mindless, with no main idea or thought process. Sketches are that beautiful grey area in between, which is what I love about sketching. Regardless of whether it is to lead up to a drawing or stands on its own, sketching is one of my favorite types of art.