Packet loss can make moving characters in the world appear like jumping around (up to your client getting a warning by anti-cheat code discovering unusual acceleration, if that is still working at all), make you miss parts of a conversation, unexpectedly die in combat, even disconnect you more or less frequently.
Reasons can range from a faulty network adapter (or broken wires to it) in your PC, internet router, or even up to mis-routing or other node misconfiguration by your internet provider; or, if you play with a wireless connection, possibly heavy interferences caused by e.g. aged DECT phones or microwave ovens. Also there was a time, long ago, when the game server software acted weird.
Knowing such statistical numbers is surely useful if above mentioned issues happen to you.