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?

I present to you the hoo-mamma of PC cases, the tube of Babel, El Capitan Lite, the 'doubles as a cryochamber', the Chonka 9000, the Compensator, the Pillar to Prometheus, the Modern Megalith, the ...