My f keys have pictures above them. On my old laptop, f5 was a refresh button. On this (windows 8, don't know if that make a difference?), it seems to disable my mouse - I keep making the same friggin' mistake and accusing my mousepad of disappearing . I don't know how accurate this link is http://ctrlf5.net/?p=264
i suspect programmers can programme any key to do any reasonable thing, but there is probably an MS suggested/recommended list in order to encourage consistency across programmes running on the Windows OS.
Back in the old days when BBC B computers were introduced into schools (remember them?), you could programme an f key to remember a chunk of text. This was very useful when phrases were regularly repeated.