The answer is very simple: When I have to run Windows programs. Support skills is very relevant to the question. Various early comments have used the phrase "It all depends on the right tool for the job". That phrase is not the whole story.
Every time you add a new OS to the mix, the support problem becomes more complex. We used to run 1 Solaris, 2 Linux, 1 NetBSD and 2 OpenBSD systems plus a whole lot of MS Windows. Over about 2 years I converted all the Unix like systems to OpenBSD. I did not convert because I thought OpenBSD was the best for everything. As long every thing worked after the conversion I was happy. I just wanted to simplify the upkeep of the systems.
