NAT is a crutch to circumvent the problem of "there are not enough addresses for each device".
I _assume_ you are referring to a default deny inbound firewall (so that devices are not reachable from the outside), but these are very different, completely orthogonal concerns (and independent of the IP version in use).
I _assume_ you are referring to a default deny inbound firewall (so that devices are not reachable from the outside), but these are very different, completely orthogonal concerns (and independent of the IP version in use).