Much bran, little meal.

The image is of grain processing that leaves a large amount of bran but only a little meal. The less desirable portion outweighs the part one hoped to obtain.

More broadly, the proverb describes something that has plenty of bulk but little value. It draws attention to the poor balance between what is produced and what is useful.

Use it to criticize an effort, explanation, or result that produces a great deal of material but very little of what matters. The contrast is between sheer quantity and useful substance.