Using alien is discouraged! Use native RPMs!

Sometimes, alien can be useful:

for a developer -- to prepare packages for hasher and other RPM-based tools when there is no other (quick) way to make an .rpm (the sources are closed or the procedure to build the binaries is not easily reproducible on Sisyphus). This is thought only as a way to facilitate the work of a developer rather than a way to produce packages that can be published.
for an administrator -- obviously, to put an alien package under the control of RPM.

Using alien for producing ALT packages

alien --to-rpm, or the short form alien -r, is used to produce RPMs.

from .deb (holding binaries)

Sometimes, it works normally: