So there are two kinds of scanning that are helpful in theory, I think:
1) Host scanning - to identify new or unexpected hosts on a subnet.
2) Auditing - seeing what's out there and routable, and comparing to your IPAM system.
SW IPAM does #1 for sure, at least for subnets you have configured. I don't know whether it can do anything for #2 though, to find new, unmanaged, subnets.
I agree though - that's really an useful thing to have.
