The point of sparging is to rinse the grains of sugars that havent dislocated and dissolved into the wort of the first runnings. Fly sparging accomplishes this by continuously running water over the grains to dislodge the sugars into the sparge water. Batch sparging accomplishes it by dumping the water in all at once (which will free SOME of the sugars, but not all), and then stirring it all to move the water over the grains and free the sugars.
So, you dont have to stir, but stirring increases the amount of sugars you free from their grainy prisons = better efficiency. I also hit 75% efficiency regularly with a batch sparge.