Lymph nodes is where lymphocytes are stored, it that simple.
It's not a "filtering system" for debris ))))
When there is an infection lymphocytes begin to replicate in order to fight it - that's why lymph nodes swell up.
Yeah, remember swollen tonsils? Tonsils are lymphoid tissue. They can swell when you have a throat infection.
Yes they swell on other infections. It depends on the location and how much infection is traveling through your body. As OrionQuest stated the lymph system acts as a filtering system and traps foreign bodies within them, causing them to swell.
Yes, that's what lymph nodes are for. Lymph nodes are like water filters for the lymphatic system. They swell because of cellular debris from your body fighting infection. Look at any child with a cold or the flu, you can feel the lymph nodes readily swollen on the neck. Of course, it's the doctor who can tell the difference.