Favourite Bakeries/ Patisseries in Paris

Someone tell me why so many of the bloody sourdough recipes ask you to culture a larger amount than you'd ever need and to throw away a large portion of what you culture instead of using a smaller amount???! For example in the Bread Bible the sourdough recipe is great. I have found if I make a double chef, and reserve 300 gr and use 300 gr what I am throwing away can feed that day's batch of bread. But the handling instructions are off in that I find that the best instructions come from Chez Panisse cookbook. Does this super starter have greater strength or something?

Happy Baking

Ryan