Since I started studying arts I have never stopped practicing life drawing because I know that the quality of my work depends on the quality of my drawing. Even when using photographs as a reference, knowledge of the human form is essential to "fill the gaps" and go beyond the poor bi-dimensional reference. Lifeless portraits are the result of mere dependence on photography and poor knowledge of the features in real life.
Nevertheless it is as easy to build up drawing skills as to lose them in periods of inactivity. I can spend months without painting after a solo exhibition, when I am in search for new inspiration, and soon my ability to put visual ideas on paper suffers from lack of practice. I always compare it with sport: if you stop doing it, you will have difficulties starting again and will be out of shape. This is why I always try to do life drawing especially when I am not painting.