much networking gets done in off work hours or over lunch, during the day the interactions are on specific topics, projects, issues etc, its when you get a chance to spend general time with colleagues is when you build relationships, sometimes its personal relarionship building, sometimes some work topic and really discussing it in depth..
its not a paid lunch, but it is valuable time, refer to a book called ‘never eat alone’ by keith ferrazzi to get some more insight into that.
I have had some fantastic meetings with my boss over lunch, its unscheduled time, talk about whatever , sometimes he is picking my brain sometimes I am running ideas by him, him introducing me to his peers and others in the company, valuable time, contacts building, relationship building and career advancing. dont underestimate it