Actually, he's right, Veebs. When it comes to breads, the ratios of levening agents, fats, flour, moisture, etc. are pretty specific for a certain result. Weighing the ingredients renders the best results. Absent doing that, precise measuring is necessary.
Cakes, cookies, and other baked goods are somewhat more forgiving when the recipes are tweaked, but customization usally falls in the add-in category (flavorings, nuts, fruits, chocolate, etc.), rather than the fat/flour/levening ratios.