Even if they had been clean since they were emptied out last winter, gutters (eaves-troughs) near deciduous trees will eventually need to be cleaned again as they collect falling leaves through autumn. Leaves may continue to fall for several weeks, and will fall more abundantly as they get dislodged by rain.
Too many fallen leaves clog gutters and downspouts. If too much debris is left in downspouts for too long, it rots and settles so that it can be very difficult to dislodge. If rainwater can not adequately drain through gutters and downspouts, it can only flow over the edges of gutters. The falling water can erode the ground below, and splatter mud onto nearby walls.
This may not seem like much of a problem, but the reason that gutters and downspouts drain rainwater to the ground gently is to keep the walls dry and clean. Damp walls are likely to rot, especially if water splatters into basement vents. This is why early American homes that lacked expensive gutters were often outfitted with dense ‘foundation’ shrubbery or perennials to soften the splatter.
Leaves that accumulate in the valleys of the roof (where perpendicular slopes meet) should also be removed. Debris can also collect on the upslope side of a chimney. Homes with room additions have more awkward spots to collect debris than unaltered homes. Flat roofs and parapet roofs are of course very likely to collect debris under trees, and may need to be raked more than once.
Vines should not be allowed to climb onto roofs. They can tear apart roofing material, collect debris, and promote rot. Likewise, limbs of trees and large shrubbery should not be allowed to touch roofs, gutters, or even walls. Their motion in the breeze is abrasive to shingles, gutters, paint and siding. They can literally grind off shingles and break terracotta tiles.
Tree limbs should also be kept clear of chimneys. Even during rainy weather, hot exhaust from a chimney can dry and ignite limbs that get too close. Pine, cypress, cedar, and palms with beards (accumulated dead fronds) are very combustible.