Use FreeBSD and OpenBSD frequently at work on servers. Compared to Linux, the systems are much simpler (u/Thundarrx already commented on what I mean) and smaller. The small size, simplicity and predictable nature of software installs makes it easier to learn (everything aside from the base system on FreeBSD gets installed in /usr/local. /usr/local even has it's own etc and etc/rc.d directories). The documentation is pretty good too. FreeBSD is FreeBSD and OpenBSD is OpenBSD. Linux is very sprawling and messy in comparison, and the multitude of distros makes a fractured landscape.

Here's my experience with the BSD personally:

OpenBSD

At work we use OpenBSD for all our layer 3 networking functions (stuff that is typically handled by propriety router hardware like from Cisco). Namely routing, firewalls and IPsec VPN tunnels. We use static routing internally and BGP routing at the network edge. Packet filtering is done with PF, which is by far my favorite firewall I have used; it's single file configuration and intuitive syntax make it much nicer to work with compared the others I have used (firewalld, iptables or proprietary things like Cisco ASA, Fortinet). Handling link fail-over for high availability on OpenBSD is simple with CARP (a similar but not quite compatible implementation of the VRRP protocol). I'm pleased with OpenBSD as a network operating system.

FreeBSD

We use this for general server workloads like http, samba, dns, dhcp email etc. But where it really shines is with ZFS on our disk arrays (JBOD attached with SAS or fibre channel). ZFS volume snapshotting and raid-z are awesome features on file shares and backup server. However, Linux is really encroaching on the workload of FreeBSD for us. The pace of development and ecosystem on Linux is so much greater, we are tending to use CentOS for more and more of our infrastructure (developers want the latest trendy software platform, so we're running Hadoop and soon docker too, neither of which support FreeBSD. Even ZFS works on Linux now too, which makes FreeBSD shine that much less brightly). FreeBSD has served us well, but as needs change, I've began to use just CentOS going forward as the preferred server platform to keep our infrastructure landscape as uniform as possible going forward. FreeBSD is great for tried and true services though, it just doesn't keep up.