As an example, there's a recipe that calls for 3/16th teaspoons of yeast. Why didn't he just write 1/4 tsp? There is no way that 1/16ths of a teaspoon make any sort of difference given all the other factors at play. This kind of faux precision abounds in the book and can make the activity pretty stressful.
It's a great introduction to bread baking, but once you get the hang of things you realize the precision he requires in his recipes is simply not called for. You can bake great bread in less time, or more time, or with cooler water, or warmer water of whatever--and have more fun doing it. (Also, his sourdough recipe is criminally wasteful).
To anyone trying to get into bread: Definitely use FWSY to get a better "feel" for dough, but as soon as you do I suggest you leave it behind. Have fun. Tartine is a great second book.