Customizable

The base installation of FreeBSD is meant to be lean and mean. It only contains the services absolutely necessary to operate the machine. Instead, FreeBSD sysadmins are encouraged to install their own services, whether from the ports tree or elsewhere, choosing for themselves which software packages suit their needs.

For example, any webmaster will need a webserver, but depending on the needs, a particular kind of webserver may be more or less appropriate. Some may need compatibility with older plug-ins of the Apache 1.x family, while others will want the greater security and speed of the Apache 2.x family. Still others yet may need the highest speed and efficiency (but with no CGI capability) found in the thttpd family. With FreeBSD it is easy, normal and even expected to pick and choose or even switch with minimal pain and heartache (or downtime).

This also holds true for FTP, DNS, mail, ssh, X-Window components and almost anything else. Even those services which do have a default system installation (such as sendmail for mail services) are specifically designed to be simply and easily swapped out with any other service the system administrator may choose. For example sendmail can be replaced by qmail with a single command:

cd /usr/ports/mail/qmail && make install && make disable-sendmail && make install-qmail clean 

Please be aware though, one must configure qmail after doing that so please don't be rash and blindly replace sendmail after reading this without being ready to learn a new system.

This is all in stark contrast not only with Microsoft Windows, in which sysadmins and users alike are tightly bound to whatever Microsoft provided in the way of system services, but with many GNU/Linux flavours too. For example, veteran Red Hat Linux admins are familiar with the notion that Apache 1.x "goes with" Red Hat 7, whereas Apache 2.x "goes with" Red Hat 8 and it can be something of a dire mess to try changing from one to the other. What's more, upgrading a base Microsoft or Linux system is likely to willy-nilly change its services whether this is wanted or not. Meanwhile, upgrading the OS may make needed (perhaps mission-critical) services inoperable and comes with widely known risks, downtime and often, unhappiness.

FreeBSD mostly succeeds in drawing a much sharper line between the base system and optional services. It's easy to install whatever type of service wanted from whichever vendor or group chosen (open source or not).

Moreover, FreeBSD is truly open and free. For highly specialized projects, the source code itself can be studied and modified. While this step is not taken by most FreeBSD users, it's a comfort.