From my limited understanding of the two commands, up is used for updating packages where updates exist, and dup is for updating packages from one distro/repo to those on another distro/repo, regardless if the version is upgraded.

On a clean install of 13.1 with no additional repos, up and dup install different packages. Specifically, up and dup both upgrade 484 packages, but up installs 18 new. dup however install 25 new. Why does dup install 7 additional packages, and are they worthwhile? Should dup be used on a clean install of 13.1?

Also, what is the best usage scenarios for both up and dup?