Most obviously, the same things as its disadvantages:) With nc, you don't have encryption or authentication, which is good - faster, no keys to set up, no fingerprints to accept - and terrible - no transport encryption, no data integrity verification, no access control except for at the network layer. Also, slight difference in how you use them: scp operates on files, nc on streams. But you can just pipe over SSH, so that's not a big difference IMO.