[OptionX]

I when to check and I think I get it now, the link-local is routeable (switchable?) but only at the local level, but then you might ask why bother with SLAAC at all then. It's due to router being unable to route anything with a link local origin or destination as they are not globally unique so if you need to talk to anything past layer 2 you need unique-local address (or global).

[anyfoo]

Yeah, but you can still talk to other hosts on the same link, not just the router, at any layer protocol. Link local addresses are not routable, but if you want to talk on the same network segment, that's fine.

[dcrazy]

Case in point, when I SSH from my laptop to my desktop using mDNS hostnames, I see “Last connection from: fe80::<something>”.