chef william, there is a reason WHY your instructor had you weigh it out.
It's all about accuracy. Ask five different people to measure out a cup of water (or flour, rice, etc.). Now, weigh these five different "cups" of water. Odds are, they will all weigh slightly different, as people measure volume different. But, a pound is a pound (or gram is a gram). Baking is all about accuracy. I've heard numerous times, that "cooking is an art, baking is a science." Baking formulations don't deviate much, to keep consistent. Not to mention if you start fiddling with a formulation without knowing what you're doing, it probably won't turn out. The only real way to have different people measure out a set amount of whatever, and get the same amount, each and every time, is to weigh it out.
Peace, Love, and Vegetable Rights!
Eat Meat and Save the Plants!