By downloading an updated Kad server list (or nodes.dat file), you are essentially giving your eMule a fresh map of active doorways to enter the network.
KAD is eMule's "serverless" network. It is a distributed hash table (DHT) that allows eMule to find sources without relying on central servers. Why does this matter? Because servers often go offline due to legal pressure. KAD is permanent. If you master KAD, you rarely need a server list. However, for initial bootstrapping, you still need servers. Download Emule Kad Server List walame