Leaves that have fallen offer shelter to insects, can be consumed as food for wildlife, used as bedding for creatures needing to make a shelter to hibernate in. They can supress the growth of weeds and help with the growth of the grass or your plants in the following year if gathered together and being allowed to decompose in your flower beds. Nature has a system and trees would not smother their roots with leaves if it were for no benefit. The leaves they have shed offer protection for their roots, keeping out the harsh cold and smothering any smaller saplings that may act as competitors for their space and light. The latter can be a problem for those wanting to keep any saplings that are trying to grow, so it is important to remove the leaves threatening the smaller trees and move these to the areas you would like to be more heavily saturated in nutrients.
Even individuals who do not have a huge interest in gardening can probably admit that at some point they are purchased fertiliser or ‘plant food’, but nature offers us free plant food every year. This is in the form of leaf mould made from the fallen leaves. To make leaf mould, gather the leaves you do not want on your lawn, or those smothering the younger trees. A lawnmower is a good way of doing this as it will shred the leaves, which helps them to break down properly. These leaves should be placed in a secure area where they will not blow away, such as a makeshift chicken wire pen, and should be left undisturbed for a couple of years. You can use them the following year, but as a mulch, not a leaf mould. Even by spring the leaves at the bottom of the pile will be converted into rich soil. You can also put your dead leaves into a compost heap which can also contain suitable food scraps, other foliage, egg cartons and cardboard.
Whatever you do, just don’t throw them away. Even just moving your unwanted leaves to a lonely, unloved part of your garden means they will have the chance to break down and be reused, no matter how long you have forgotten about them. Anything is better than them being put into plastic bags which then pollute the surrounding earth.