Both were important. Formal discussions and things on the agenda were great for seeing the general state of the art and how people were doing things and how our lab could improve, as well as going through the list of sessions and saying 'oh wow that looks fascinating' and getting exposed to new ideas. But my own research got the most direct benefit from unstructured talking with other researchers and people seeing my name and research on the list of posters and coming by to talk, and vice versa.