Profit, Benefit, Advantage
Cut grains with a knife to make them smaller and you'll make a great profit. By cutting them, now you can get three grains worth of money for what was once a single grain.
Imagine buying some rice. Now cut all the grains with a knife into smaller grains. Now sell them for two, three, four times the profit!
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To make an even better profit, you decide to cut up reeds (り) too. You stuff the grains in the reeds and sell that as "self-cooking" sets.
Picture all of your reeds full of grains in a row. The entire world will benefit from your crafty invention. And you'll turn a great profit too, which certainly doesn't hurt.