I noticed that IPv4 reserved 169.254.0.0/16 and IPv6 reserved fe80::/10 for link-local address. While I saw IPv6 uses both fe80::/10 address and my private IPv6 address fd00::12 to communicate with other devices in Wireshark, I never seen 169.254/16 working in IPv4.

So, what is the purpose of link-local address?