djdarko: Yes, that turbo button actually made it run like 10x faster. I can't remember any real reason to turn it off.
Actually it's funny because the turbo button was actually there to take a fast CPU and slow it down to be able to run old software that didn't work properly with faster modern programmers, but the marketing people decided that having a "snail" button wasn't nearly as good of a marketing idea as having a button labelled "turbo", so that's what stuck. :)
If you run various video games back then on native hardware many of them fail due to using timing mechanisms that were tied to the CPU frequency which of course varies from CPU to CPU. I remember one such game was MS-Pacman for MSDOS, you would start a game and in less than a fraction of a second all 3 of your lives would be killed from the game running at Mach 5000. LOL The turbo button was intended to drop the CPU frequency down to allow more old software like that to be still usable, but over time with computers continuously getting faster it became impractical at a certain point and ended up getting dropped from the standards PC system builders use when designing new systems. It was for the best though as it had become a rather useless button by the year 2000 or perhaps earlier even. :)
Nowadays things like DOSbox make running older software work a lot better anyway. ;)