In the 80s and 90s, some desktop PCs included a "Turbo" button, but what it actually did was a little unclear. What was it for and why don't PCs have them now?

The PC turbo button and LED clock speed display were common features on early personal computers. Wanting to add a little retro chic to his modern battle-station, [Matthew Frost] assembled a charming ...

What does that button do? I used to just keep it pressed..i dont see why they decided to include a "turbo" button, why would anyone want to run their computer below max speed? Ive also noticed ...