The whole income should never be spent. It's important for kids to save back a set percentage for the future. Americans are too accustomed to spending every bit of available income, then borrowing more via credit. Teens can learn to live on their wages, save for a rainy day, and thus prevent many future financial disasters. Of course, this lesson is authenticated by parents who are good stewards.
Kids can also learn to limit hobbies and sports to affordable items.
Our son, Sam, has a rather expensive exotic pet that often requires veterinarian expertise and must be boarded at a pet store when we leave town. One stipulation for getting this animal was that he agreed to pay all of the dragon's expenses out of his lawn-mowing money. This creates incentive to keep Draco in top health. Sam also shows neighborhood kids how to properly maintain their pets' health. He boards their exotic pets when they go on vacation, giving proper care to diet and lighting.