Grasscycling is the practice of leaving clippings on the lawn when you mow it. Why is this a good idea? Because grass clippings:
contain moisture so you won’t need to water your lawn as often;
contain nutrients that your lawn needs, which can reduce the amount of fertilizer you need to apply; and
breakdown quickly and easily.
Here is an excellent link that goes into depth about grasscycling.
To help you with grasscycling, you might also consider this excellent tool: a mulching mower. According to the CalRecycles website, “Mulching or recycling mowers make grasscycling easy by cutting grass blades into small pieces and forcing them into the soil. You may also want to consider purchasing an electric mulching mower to reduce air pollution.”