Artists are always looking to improve their skills and sometimes that requires studying life as it is rather than other interpretations of life, and so they often seek out a model to draw and thus learn how to better draw actual figures. Male life drawing allows an artist to draw a human figure and thus look at other ways to draw the human body for other projects.
The posing helps them do better draw the human form, making them aware of different issues of the human form. A human body can be large or small, smooth or defined, and all points between. An artist needs to view a human body so that they can better draw a more realistic form; this makes posing something that an artist needs in order to become better at their craft. By drawing they can only become better at what they do and thus perfect their craft.