and it had Turbo button, which did absolutely nothing

These old 'turbo' buttons actually did do something -- they limited your CPU clock speed.

Because some old games (and perhaps other software) relied on counting CPU cycles for timing the game. The faster your CPU, the faster the game would run, and the faster things in the game would happen. When CPUs got too fast for this, such games became unplayable because everything was happening in such fast-forward speed that the player could never hope to keep up. The counter-intuitively named 'turbo' button would bridge a jumper on the motherboard and change your CPU clock speed to a lower value, slowing it down so these old style games could still run at a reasonable, playable pace.

Ironically enough, the 'turbo' button made your PC slower.

(Personally, I think turbo buttons are due for a comeback, but as fan control options. Use a 'turbo' button to switch between fan control profiles -- turbo off for quiet profile, turbo on for maximum performance profile.)