WHAT DOES SOLAR PANEL HAMNESS MANUFACTURER MEAN?

With Daisy Chain you receive a regular wiring, while Leap Frog will save funds on wire and reduces power losses produced by warmth, being essentially the most economical wiring method. this is the dumb issue but I’m not solar panel savvy. What do the rubber plugs at the conclusion of solar panels do? Are they required? I have 3 which might be