confusing!

I been wondering about the amount of yeast when making a dough with a poolish or pre ferment.

According to the the bakers's percentage, you need to add the same amount of yeast when using a pre ferment or not.

But..I thought the yeast in the pre ferment multiply as time goes by. Why add a another bunch of yeast when making the final dough?

Would you add less yeast than in the recipe when making the final dough?

By adding the amount of yeast in a recipe, the rising time will surely fasten but wouldn't the bread taste yeasty?