Painting and sketching are the ways to express yourself. For some people it is their obsession, for others it is a way to relax their minds. While others consider it a way to make a connection with their inner-self. In any case sketching and painting are something intricate yet soothing and fascinating.
I believe that to display your art you do not have to be a great artist. You just have to draw you emotion and personality on paper.
I am not a painter but i believe any passion is a stress reliever. Painting and/or sketching needs focusing your mind, time, effort and emotions thus you tend to forget other things and it really relaxes ones mind.