It's fortunate for me that we have tolerant neighbors (referring specifically to neighborhood humans). I do try to keep the front yard up to reasonably civilized standards--easier to do since Piet Oudolf and James Van Sweden made ornamental grasses and seed heads not only respectable but trendy in some circles--but I am about as fond of raking leaves as I am of mowing grass or trimming yew hedges: that is, not at all. As a result, most of the front-yard leaves (of which there aren't many, as that's the sunny side of the lot) get raked under the rhododendron or out to the compost pile, but this year the back has not been raked.
There are reasons for this other than my general laziness. For one, we still have a scraggly, unattractive turfgrass mix left from the previous owner's attempt to grow lawn on the back slope, and the sooner it dies, the happier I will be. Turfgrasses do not like being smothered in leaves, so my hope is that we can accelerate the process of making the back yard more interesting.
Second, most of our leaves (with the exception of those from the neighbor's sycamore) come from oak or maple trees, trees which, according to entomologist Douglas Tallamy, attract more lepidoptera than almost any other plants (over 500 species!). This means that a good percentage of those leaves are likely to contain butterfly eggs, eggs that will not hatch if we put their host leaves in plastic bags and send them to a landfill. The eggs might survive mowing the leaves so that they break down faster, but why risk the loss of next year's hairstreaks and duskywings?
Third, leaf litter has a number of important functions, especially in forest ecosystems (though our back quarter-acre hardly qualifies as "forest"). The spring wildflowers of the eastern woodlands require a rich soil in which nutrients break down slowly, and allowing leaves to decompose at their own pace is one of the best ways to create that soil. (One of my fantasies is to have soil that will support trilliums, which right now our yellow clay will not--but maybe in twenty years or so....) Some insects overwinter in leaf litter, including mourning cloak butterflies, wooly bear caterpillars, hummingbird moths, and certain bumblebee queens. I've never seen an amphibian in our yard, but if we ever get tree frogs, they prefer to spend the winter under leaves. This year, we have had brown thrashers thrashing in the leaf litter under the few remaining backyard yews (and despite my love for butterflies, I do not begrudge our thrashers anything they can find to eat).
My messiness, I must confess, extends to not whacking things back as early as many people do, but sometimes that hesitation is rewarded. We have birds feeding on seedheads in the meadow garden, and the wild tangle of our in-need-of-pruning lonicera sempervirens has become a favorite perch for wrens and juncos. The specimen on the compost area fence attracted the first fox sparrow I had ever seen.
The moral of the story: one species' mess is another species' home sweet home.