I had one and used it on occasion. I had some games that were just too fast at the 7.x MHz speed and needed the 4.7 MHz speed to be playable. Otherwise it was always at the turbo speed.
Back then, programs were usually written to do the next line of code as soon as the computer is ready. Only later did programs get more sophisticated and were told to wait until the clock reached a certain time to do that code.
Consider a typical golf program. You pressed a button to start the backswing and released it to stop the swing (and hit the ball with that amount of power). On a slow computer, that would take 1-2 seconds. But on a faster computer it may take 0.5 seconds -- too fast for a player to accurately do the motions. Thus, you'd turn off the turbo, slow down your computer, and make the program usable again.
For many programs (like an office program), turbo is useless because CPU speed isn't a concern.
It underclocked your CPU when you wanted to go slower. That is, your CPU was at a higher speed than most programs were intended to run on, and thus these poorly written programs would be unusable. You could press the button (turn off turbo) and then run those programs without problem.
Back then, programs were usually written to do the next line of code as soon as the computer is ready. Only later did programs get more sophisticated and were told to wait until the clock reached a certain time to do that code.
Consider a typical golf program. You pressed a button to start the backswing and released it to stop the swing (and hit the ball with that amount of power). On a slow computer, that would take 1-2 seconds. But on a faster computer it may take 0.5 seconds -- too fast for a player to accurately do the motions. Thus, you'd turn off the turbo, slow down your computer, and make the program usable again.
For many programs (like an office program), turbo is useless because CPU speed isn't a concern.