They always did something; the Turbo button was switching the CPU frequency on older PC's that ran software with no speed auto-dectection and adjustment. On IBM PC XT the turbo button was switching between 4.77 and 9.54MHz, on AT it was 8-12 or ever 16 MHz. They were needed on faster computers because some games were otherwise unplayable at the higher frequency.
You may have had a turbo button on a PC case that was not connected to anything, that is a different story. If you put a 486 in a case from a XT the turbo button "not working" is your fault only.
So the question is.....why weren't those machines running at the higher frequency in the first place? Why would you only enable the turbo mode to play games but no to work in Excel?
Energy efficiency/consumption would be my first thought.
The games were unplayable at the higher frequency, presumably because they made some sort of assumption about the relation between clock speed and play speed. Typically the computer was on "turbo" all the time.
The turbo button made the machine slower for compatibility with older programs, as described in the parent post.
It's actually the other way around. You'd have to disable the Turbo to play the games. Because they where synchronized to the slower cpu clock frequency. For your spreadsheets you would use Turbo. Marketingwise it mirght make more sense to have a button to make your computer faster instead of one that makes it slower.
On AT computers you had to go to low frequency to play games built for XT's. For example M1 Abrams tank simulator was a slideshow on a XT at 4.77, slow but almost playable on 9.54, fine on a AT at 12 MHz and unplayable on a 386 at 40 MHz (it was like a movie played on 10x speed). On the 386 with turbo off (16 MHz) was playable.
>They always did something
No, many did nothing. I remember pulling PC's apart to find the switches not connected to anything.
A button not connected to the motherboard is not a fault of the button, but the builder of that computer, is it?
I had a Turbo button on a 80386, I believe it brought it down from 25 MHz to 12 MHz. I think they were still common on 486s too though, it wasn't until Pentiums that the option stopped being included.