Autumn foliar color certainly is pretty while it lasts. Although less prominent locally than it is where cooler weather begins earlier, it is an asset to many home gardens. It generally appears a bit later within mild climates here, but might also remain suspended a bit later. Ultimately though, with enough wintry wind and rain, it eventually becomes foliar debris.
Evergreen foliage also contributes to the mess. It is likely less abundant than deciduous foliage is during autumn, but only because it sheds through more extensive seasons. For example, Southern magnolia sheds mostly through spring, as new foliage replaces older foliage. It then continues to shed additional debris throughout the year, including autumn.
Regardless of its various origins, foliar debris becomes more of a concern during autumn for two simple reasons. Firstly, and obviously, more of it accumulates during autumn than during any other season. Secondly, since autumn is the beginning of the rainy season, it is the most inconvenient time of year for such debris to accumulate within home gardens.
Roadside gutters, eavestroughs and their downspouts should drain efficiently. However, foliar debris can interfere with their drainage when it becomes most important. Roadside gutters are more accessible, so are easier to observe and clean. Eavestroughs and their downspouts may be beyond reach, but may need more cleaning if defoliation continues.
Foliar debris is unhealthy for turf, groundcover and shrubbery that it accumulates over. It inhibits photosynthesis by obstructing sunlight. It can also promote proliferation of fungal pathogens. This is why prompt raking is very important. Foliar debris can stain pavement and decking, and may be hazardously slippery. Behind chimneys, it can promote decay, and possibly become a fire hazard.