You can use both, to an extent. My most recent example: The documentation for GNU troff (groff) in Debian is incomplete-- the man page for eqn(1) includes the GNU extensions mostly, but not the basics. So I downloaded the OpenBSD manpages which includes complete documentation for eqn(7).

https://ftp.openbsd.org/pub/OpenBSD/snapshots/amd64/man72.tg...

Good documentation is a killer feature, in my opinion. It's nice they provide it all in one tar ball.