The good old-fashioned rocket jump is another example of this.

Quake 1 had a feature where if a player took damage, they'd get pushed in the direction the damage came from. This was originally intended to serve as a visual indicator.

Of course, this meant that if you aimed the rocket launcher at your feet, and jumped and fired simultaneously, the damage kick + the jump would launch you a good distance upward. This became a popular enough technique that it was retained in the Quake sequels, and even imitated in games like Half-Life (the Gauss Gun would push you backwards, allowing a "rocket jump" of sorts)...