Sketchbooks are an artist's best friend, you can carry them around, and sketch things out in public, or just from your imagination. The paper of a sketch book is not like normal paper, and is much thicker to cope with the vigorous action, as well as the longevity someone might require from a finished piece. They are suitable for various mediums of art, including pencil, chalk, charcoal, ink and more.
Leather bound sketchbooks are extra durable too, giving you that extra protection for your sketches and work when out and about, going to the places that inspire you the most.