What are the "Scroll Lock" and other keys on my computer for?

The Straight Dope after a long description of various keys and tricks concludes: One suspects that some oddball keys were put on the PC keyboard (or to be more precise, included in the ASCII character set, most of which found its way onto the PC keyboard) because the developers figured they'd come in handy for something.

On the whole that has turned out to be the case--programmers and developers have found a use for nearly every key on the keyboard, even if that use isn't obvious to the general computing public.

Witness the tilde <~>, which, whatever use it may have as a diacritical mark, now can mean "home directory" or "text omitted," among other things.

Given the pace of change in information technology, there's a lot to be said for designing your user interface for maximum flexibility.

For more complete answers to this and many other questions see The Straight Dope.