Link local addresses have a scope limited to the network segment of the holding interface. In IPv4, link local range is 169.254/16 and in IPv6 range is fe80::/10.
IPv4 link local addresses are used in most cases when automatic IP addresses is desired for a specific interface, but there is no DHCP server to assign IP addresses.
IPv6 link local IP addresses have a broader usage specially in data center network segments where routing protocols such as OSPFv3 and RIPng can run between link local addresses instead of global/organization addresses.
Another use case for link local addresses is as next-hops for static routes.
List ipv6 neighbors in Junos CLI
> show ipv6 neighbors IPv6 Address Linklayer Address State Exp Rtr Secure Interface 2001:470:1f15:72b:1:0:22:2 00:0c:29:6b:1a:15 stale 1113 no no vlan.22 2a02:2f0f:27::22:2 00:0c:29:6b:1a:15 stale 972 no no vlan.22 2a02:2f0f:27:26::2 00:0c:29:e9:71:60 stale 1066 no no vlan.26 fe80::1 00:15:63:40:4c:40 stale 780 yes no ae1.5 fe80::20c:29ff:fe03:a588 00:0c:29:03:a5:88 stale 686 no no vlan.8 fe80::20c:29ff:fe6b:1a15 00:0c:29:6b:1a:15 stale 836 no no vlan.22 fe80::20c:29ff:fee9:7160 00:0c:29:e9:71:60 stale 1052 no no vlan.26
IPv6 static route to a link local next-hop in Junos
In order to use a link local address as next-hop for an IPv6 static route, the interface is a mandatory parameter of the static route due to the nature of link local addresses. Interfaces next-hop can be specified only for qualified (alternate) next hops.
> configure Entering configuration mode # set routing-options rib inet6.0 static route ::/0 qualified-next-hop fe80::1 interface ae1.5