* privacy addresses are great * deriving additional addresses for specific functions is great (e.g. XLAT464/CLAT) * you don't get collisions when you lose you

* privacy addresses are great * deriving additional addresses for specific functions is great (e.g. XLAT464/CLAT) * you don't get collisions when you lose your DHCP lease database * as Brian says, DHCP wasn't quite there yet when IPv6 was designed * ability to proactively change things by sending different RAs (e.g. router or prefix failover, though these don't work as well as one would hope) * ability to encode mnemonic information into those 64 bits (when configuring addresses statically) * optimization for the routing layers in assuming prefixes mostly won't be longer than /64 … and probably 20 others that don't come to mind immediately. I didn't even spend seconds thinking about the ones I listed here.