Turbo mode reduces the number of times the stage in Scratch is redrawn, making calculations and other processes faster. This can be very useful indeed. Be aware that the Scratch turbo mode is around ten times slower than the turbo offered by the new flash player on the Scratch site!
Since this is a question about Scratch and not a greeting thread, I'm going to move it over to the "Questions about Scratch" Forum where you should ask any questions like this in future
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Take a look at this article, in the wiki, for a little more information.
You can start Flash Turbo Mode by simultaneously pressing the shift key and clicking the green flag while using the Flash player.
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