I'm often asked about the importance of gesture drawings...usually 1-2 minutes sketches of a model. I'm going to include here what wikipedia says...yes they have an article on gesture drawing! What they say is great and all true but I would add that for me, it helps me to better draw longer poses in proportion. Under most of my longer studies, there is a gesture drawing...sometimes lightly sketched and barely visible, sometimes visible and sometimes, the gesture drawing, or parts of it, are visualized but not rendered. Whichever the case, it helps me get a look at proportions and placement of various parts of the body before working on the finished drawing.
The primary purpose of gesture drawings is to facilitate the study of the human figure in motion. This exploration of action is helpful for the artist to better understand the functions and exertions of muscles, and acts as a foundation upon which more sustained observations may be based. The practice allows an artist to draw strenuous poses that cannot be held by the model long enough for an elaborate study, and reinforces the importance of movement, action, and direction, which can be overlooked during a long drawing. Thus, an approach is encouraged which notes basic lines of rhythm within the figure, which may be expressed through contour (line) or mass (value). The rapidity of this routine suggests an aesthetic which is most concerned with the essence of the pose, and an economy of means in its representation, rather than a careful study of anatomy or form.
For the artist, there is a calisthenic logic: just as an athlete warms up before exercising or participating in sports, artists use gesture drawing to prepare themselves mentally and physically for a figure drawing session. Because drawing (and especially figure drawing) is generally performed using the full arm, it also serves to "loosen up" the arm so that it won't tire as quickly during a life drawing session which may extend for several hours.