i'm guessing your on a yz 80?
fanning the clutch helps you feed more power to the rear wheel when the engine starts to bog down. it helps when coming out of turns, coming up hills or any time your engine sounds like it might die.
when you pull in the clutch, the engine starts to rev and pretty much clears out the cylinder. you don't have to pull the lever in all the way, just enough to get the motor to rev. again, it's basically just used when the engine is under alot of load.