Why do artists sketch?

Looking at Art:

Many of the artists who introduced abstraction into painting drew beautiful realist sketches. For example, Picasso and Matisse who made some very abstract paintings with distortion of color and form, made many beautiful and realistic images when they sketched. Have you seen these types of drawings included in exhibitions of paintings? So why is this and why do artists make sketches? If art is a language involving communication with images, then sketching is an important process for practice in seeing, representing what is seen and documenting ideas which may result in future art making.

Work in the Studio:

My sketchbooks are portable studios. I take them when I travel so I can draw new places and people and I fill them with drawings from life. I also do thumbnail sketches occasionally, to get ideas on paper for studio work. When I moved from Connecticut to Florida, I had to decide what sketchbooks to save. There was a pile of them in my studio somewhere between two and three feet high.

Sketch of the Louvre, 6”x12”, pen and ink