Why is weight the preferred method of measuring ingredients in the professional kitchen?

Question

How to make food for breakfast 

Answer 1

Mark's answer is absolutely correct. However, the majority of the professional kitchens I've worked in used volume measurements for both dry and liquid ingredients unless the outcome of the recipe depends on the measurements being extremely exact (think Yorkshire Pudding). The baking and pastry department was the only part of the kitchen (in my experience at least) who used weight measurements on a regular basis due to the necessity of exact measurement.

Answer 2

Some ingredients can pack over time reducing the volume. This makes consistent measure by volume unlikely.