I realized a while ago that sketching is a good exercise for developing observation skills and, more generally, memory. It requires full concentration, because the subject is usually not standing still, and one needs to be able to consciously think about which features of the subject are essential and which are superficial. The deliberate thinking is important, because it is the mechanism that allows committing the visual information to long(er)-term memory. The short-term memory (the one in which information lives for a couple of seconds) is not sufficient for preserving the visual details until they can be captured on paper.
Lately, I’ve been recording video highlights to supplement lectures in my Advanced Fluid Mechanics course, and one of those is about the importance of being able to make conceptual sketches of flow features for understanding of the underlying physics. Incidentally, one of the forefathers of studies of fluid mechanics was Leonardo da Vinci, whose approach was based on (some would say it entirely consisted of) observation and sketching of the natural phenomena. We are not aiming at Leonardo’s level of artistry in my fluids course, but observation is an important skill for a scientist and an engineer, and sketching is way to develop it.
The book I am recommending in the video is “Boundary-Layer Theory