. . . and has been for 33 years. I am addicted to it. I prefer it to painting. It is a rush every time. Especially from life. But, to be able to sketch from life and do it quickly, you must develop a different approach to drawing than photo realism, which is mostly what I see in the drawing world today. (Not that that is so bad.) I see very little emphasis on it anywhere, and very little understanding of the techniques needed to pull it off.
Sketching was a very important part of my training, and was taught with utmost discipline and structure, a far cry from the "blind gesture drawing" touted in art classrooms today. We followed a very strict procedure until we learned the basics of line technique, blocking in and shading. This was required before we were moved along into painting of any sort.
I hear almost daily, "I wish I could do that!" I spent seven years of my childhood Saturday mornings learning how. It didn't just happen, and I did not just teach myself. I would not be a sketch artist today were it not for that training.
I was once labeled a "street artist" by an insensitive family member, which to me smacked of an insult, like I was some peddler on the street with a plate on the walk asking for a handout for my work. I have always paid my rent (well not always!)
I consider my work (portrait sketching) a lifetime passion, and a specialty that requires the utmost dedication and sacrifice if you want to stay on top of it.