In the eighties "turbo" was all the rage and I kid you not, everything had the label "turbo" on it. Now it will be "AI" all over things.
Hold on to your hats boys and girls who were not alive in the eighties, it's gonna be wild...
Some games/software expected/relied on a certain CPU speed to run correctly. If your computer was faster than that, the software would run too fast. The turbo button let you toggle between the maximum speed your computer could go, and the speed that the software needed/expected in order to run normally.
Basically, there was an actual reason for the turbo button, it wasn't just marketing on computers.
Indeed. As a silly example, I had a Pacman clone game that ran based on CPU cycle speed. I needed to turn the in-game speed setting way down and toggle turbo off to make it slow enough to be playable.