Liquid should always be measured by volume and solids always by weight. Except those tiny quantities where they cannot be measured by a scale (like teaspoons/tablespoons or less).
Keeping in mind that 90% of recipes call for measurement by volume, so you are stuck anyway.
Baking (especially professional bakers), always use weight for ALL measurements. It is definately more accurate. It is less important when cooking to measure by weight than when baking.