What does the lymph nodes do for you?

A lot!: Lymph nodes are organized aggregates of lymphocytes with the main purpose to detect and inactivate foreign antigens arriving via lymph, collected principally from those organs in major contact with the environment (skin, respiratory and gastro-intestinal tract). They are involved in mounting a destructive response to the antigens and clearing them from the system.

Monitoring Centers: Lymphatic system absorbs/carries things too big to go into the arteries/veins like bacteria eaten by white cells and digested food. Lymph nodes "taste" the lymph for anything bad like bacteria, viruses, cancers, etc. When it detects a problem, it alerts the immune system and your body reacts. They enlarge in response to the inflammation they create when they react. They shrink when all is well.