Why choose Free/OpenBSD instead of Debian, CentOS, or any other distro?
Less churn -> the OS respects the time you invest in learning the system, and the time people have invested in documenting the system.
One is a full cohesive OS. The other is just a kernel with all the other bits packaged together by other groups of people.
And it shows.
What do you use Linux for?
For FreeBSD, given that it fulfills the tasks required:
* Ease of management - more holistically designed.
* Rock solid parts that fits together - more holistically designed.
* ZFS, jails, bhyve, dtrace, ports.
* If it works today, it works tomorrow.
* A more approachable community (which AMD says is the reason why they are developing for FreeBSD before Linux now).
* Transparency and simplicity of how it works - if you can understand it, you can manage it and fix it.
* Documentation.
* Fun! Linux is not fun.