The (possibly long and boring) story of the SysRq key.
I work on systems where not only I, but many of my users use the SysRq, Prnt Scrn, and all the function keys every day. Try running a 5250 emulation program to access an AS/400 as a terminal. All of those keys get used pretty regularly.
The original IBM PC keyboard had a one for one key correspondence for the keys on the original 5251 terminal, which was used for the System/34 and System/38 (and its later incarnations on the System/36 and the AS/400). That is, it had the same number of keys, in the same relative positions, even if some were labeled differently and had different functions normally.
IBM seems to have assumed that one of the big uses of PCs would be as terminals for these midrange boxes. And indeed, the only thing I personally used PC for during my first two or three years exposure to them in the mid 1980s was running 5250 terminal emulation. In our opinion, having grown up on midrange boxes, the little PCs simply weren’t much good for anything else.
When you started the terminal emulation program, it remapped the keyboard so that the PC keys all took the functions of the keys from 5250 keyboard that were in the same physical position. “Enter” became “Field Exit”, the right had Ctrl key became “Enter”, and so on. It was pretty easy to remember which keys did what function because they were all in the same physical spot as they were on a real terminal. This made the original PC keyboard very easy to use in emulation mode for anyone who was used to the original terminals.
But when the PC AT came out, it had a different keyboard layout than the original PC and PC XT. In an effort to help the users (at least that’s what we always assumed) IBM added labels for some of the commonly used key functions in terminal emulation programs, since the keys were no longer in the same exact positions as the keys on the real terminals.
On midrange boxes there is a specific function called System Request that you called to interrupt the current job and temporarily suspend it for various reasons; executes some command or other program then return, cancel the job, respond to a system message, etc. Depending on what you were doing, this key could get used quite a bit.
So one of the keys they added a label for on the PC AT keyboard was the System Request key, which they labeled, not to surprisingly, SysRq.
About the only reason to use it today is if you happen to be running green screen apps on an AS/400 through terminal emulation. But of you are, you are pretty much guaranteed that at some point you will use that key for its original intended purpose, to issue a system request to interrupt the current job.