what do they collect leaves for to use for what?

Dried leaves are an abundant source of organic matter that can be used for several purposes in a garden, lawn and elsewhere. The leaves can be shredded into fine pieces and used as mulch around trees or other plants. They can be added to a compost bin to complement other nitrogen-rich materials and break down into compost. In the correct proportions, the leaves can be added directly to the soil, where they will decompose slowly over time, making the soil rich. Depending on the exact type of leaves, they also can be used to make decorative arrangements or as bedding for worms along with newspaper or coir.