Nature's autumn bounty of fallen leaves isn't usually a problem for lawns and gardens, and mulching the ground with them actually helps to feed the soil for a healthier yard.
If you grew up in a neighborhood with lots of trees, chances are you had to put in plenty of hours each fall raking them all together, bagging them up, and then sending them off somewhere, most likely to the landfill. And you were probably told that the reason for this was not only so that the yard would look 'tidier' but also so that the leaves wouldn't kill the grass. This myth has probably sold more rakes and bags than anything else, and while raking may have enriched the pockets of neighborhood kids (assuming you got paid to rake leaves), the practice actually removes important nutrients from the yard, which homeowners then usually repurchase, in another format, in a bag or jug of fertilizer from the local garden center.
Well, we're older and hopefully wiser now, so the idea of removing this important annual input to our local soil biology, and sending it elsewhere, likely to the landfill to be buried instead, doesn't make nearly as much sense now as it might have back before we knew better. And while it is at least partially true that excessive amounts of fallen leaves can smother areas of a lawn when they're left in thick piles all winter, leaving the leaves on the ground as mulch can actually be an effective method of building soil and supporting a healthy yard.
Fallen leaves, as an additional physical layer of organic materials above ground, provide food, shelter, and nesting or bedding materials to a variety of wildlife, as well as overwintering protection for a number of insects, all of which work together to contribute to a healthy yard. The soil itself is also a beneficiary of this autumnal gift of fallen leaves, as the leaves are essentially composted over time into nutrients that feed both the next year's 'crop' of grass, but which also feed a vast number of microbes in the soil, which are actually the most important 'crop' you can grow, considering that all plant life in your yard depends on a healthy soil biology.
According to National Wildlife Federation Naturalist David Mizejewski, “Fallen leaves offer a double benefit. Leaves form a natural mulch that helps suppress weeds and fertilizes the soil as it breaks down. Why spend money on mulch and fertilizer when you can make your own?”
However, just leaving the leaves to lay where they fall in the autumn (see what I did there?) isn't the most effective way of getting the most benefits out of them, as sometimes they can really pile up in areas where they may effectively smother a section of the yard, but there are a number of different ways to approach your leaf harvest, depending on your particular situation.
As one plant and soil specialist, Dr. Thomas Nikoai of Michigan State University, put it, leaving the leaves on the lawn is " ... not only not a problem, it's awesome." According to an interview at Christian Science Monitor, Dr. Nikolai says that by mowing over the fallen leaves to turn them into smaller pieces, the leaves will actually enhance the lawn's fertility, not kill it off. And while it's usually recommended to use a mulching mower, or a mulching attachment, to convert the larger leaves into smaller-sized particles, virtually any mower can do the job, and it's merely a matter of mowing over the leaf-filled yard a few times during the season.
However, if you're cultivating a 'tidier' look to your lawn, and don't want those pesky dried leaves getting in the way, they can be raked into garden beds, flower beds, or as a mulch around trees, either as-is or by using a bagger on your mower to collect them. Covering garden beds with a thick mulch in the fall can be an effective and simple way to build soil fertility, as well as helping to keep the yard look tidier.
And far be it from me to encourage you to use lawn equipment in a way that it's not intended, but I've heard that you can put leaves into a large trash can and then use your weed-eater in the can to slash the leaves into tiny bits for use as mulch.
Leaves can be a great additive to a home compost pile, and by keeping a pile of it next to the compost, leaves can be used to cover layers of kitchen food waste throughout the winter. Fallen leaves can also be used to reclaim sections of the yard that are marginal, just by building a huge leaf pile there and letting it sit all winter. By the spring, the lower part of the leaf pile will be converted into rich soil, while the middle and top layers can be used as mulch or dug into spring garden beds as a soil amendment.
If none of these uses for fallen leaves work for your situation, you can look into local options for leaf drop-offs, where this yard waste is collected at a central location and then turned into compost and mulch, and although this option does still require raking and bagging, it can keep this potential natural resource out of the waste stream.
And if you're like me, and you're always looking for sources of free organic matter to use as compost and mulch and soil-building materials, you can try putting your name out there as a prospective drop-off location for neighborhood leaves. You can also contact the coordinators of the local leaf drop-off and ask about getting bags of leaves for free from the event, which I've done before, and which can be an effective and simple ingredient for enriching your soil.