Some fascinating stories in this discussion thread.
It starts with discussion about computers overheating, but about halfway through the thread, it switches to discussion of mainframe installations in which it was apparently typical to have an emergency power off button that was big, conspicuous, placed in a very visible and easily reachable location, and basically had everything short of a 'PUSH ME' sign over it. Needless to say, these buttons often got pushed, with results that make amusing stories after the fact.
Why exactly were these buttons there? The guess that comes to mind is that the installations were designed by engineers used to other kinds of industrial machinery, such as gears that could catch and mangle an unwary limb, or pumps transporting toxic or flammable fluids, where an emergency power off button could have safety benefits, and they kept the habit. But is there any reasonably probable scenario where there would be a safety benefit from powering off a mainframe a few seconds faster?