After experimenting with a few recipes from the BBA, I'm wondering what is the role of preferments (such as the poolish i mostly use) and soaker.  The author frequently mention that they are meant to extract more flavor from the grains, but this seems a bit vague.  Here are some questions I've been asking myself lately and I would love to hear the opinions of more experienced (better educated!) bakers:

1) what type of flavor is extracted by a pre-ferment?  Are the natural microorganisms of the flour contributing to this flavor (thus explaining the use of very small amount of yeast)?

2) Is the goal of a soaker mostly to soften the bran and other "hard" part of grains?  Is it to give more time for the enzyme to produce some simple sugar from starch?  In some way, isn't any pre-ferment also a soaker?  Would it contribute any flavor if used on AP or bread flour?

3) What is the role of the flour that is added directly to the dough?  Wouldn't it make sense to use all the flour either as a soaker or preferment if this is positively contributing to flavor?  Would it be "too much"?

If some recipes call for both (sometime on the same type of flour, such as in the 100% whole wheat bread from BBA), then it suggests that they contribute different flavor profile.