The chapter? What chapter would that be? This isn't homework is it?
NIS provides centralized user management, so with NFS the files owned by a known user on the server will also be known to be owned by that user on the nfs client side. Otherwise you can have different users with the same uid, or unused uid's altogether. by pulling the users from a common services, a file will always be owned by the right person.
As for Samba, that handles users very very differently. NFS uses POSIX compliance, i.e. base level unix compatability, however as samba is for windows connectivity this doesn't occur and whilst there are plenty of ways to forge mappings between widows and unix users on either side of samba, it is a lot more work.