I used tools from the FreeBSD Ports Collection in four areas: in the network, where the operating system has very little impact on how software behaves; for remote security testing and performance testing in order to manipulate remote machines over the network, regardless of the operating system; for disk imaging of Windows, Linux, and FreeBSD machines; and on the webserver, where Twiki was my collaboration tool of choice.
Because the installation procedure for all of these tools is standard, I spent relatively little time installing and configuring my tools. Because all the tools were hosted on a single platform, I had all of my configuration and diagnostic information located in just a few places. I kept all of my potentially dangerous security tools on a single machine, which made my presence on the network tolerable to the company's network management staff. And the compatibility between FreeBSD versions made it fairly simple to upgrade and to manage multiple FreeBSD machines. And of course, I could rely on the correctness of my test results, because the system itself is so reliable.
I have tried using Linux in a similar way, but my experience is that package management quickly becomes tedious if not overwhelming. The FreeBSD Ports Collection handled that for me. And many of these tools are simply not available on Microsoft Windows. And when they (or their equivalents) are available, their cost, both financial and in terms of overhead, was simply too high.
FreeBSD's simple installation procedures and robust Ports Collection makes it easy to experiment with the huge number of tools available. I often find myself browsing the Ports Collection looking for interesting applications to install, just to see how they work. (I found Ettercap by browsing the Ports Collection, a tool that became very useful very quickly.) It became clear that the more tools I used on FreeBSD, the more economical became the management of those tools.
The next time you need to reach into your toolbox for some sophisticated, reliable, and powerful testing tools, I hope you find them in FreeBSD.