For any creator of visual images, drawing is pretty much a fundamental. This is particularly true for artists who paint with some degree of realism, but those with more abstract styles also use drawing and sketching as an extension of thinking. In a few moments it's easy to map out an idea with a thumbnail sketch that captures the essence of what you may want to do.
I use drawing this way all the time but also like taking sketchbooks on trips. Each sketchbook becomes a valued and treasured resource for future studio paintings or simply as an end in itself. The looseness of sketching in notebooks has its own particular attraction and is a wonderful way to create a personal image-based diary.