At this time of the year, a large part of my gardening day is spent clearing up leaves. - I've been asked recently WHY? - so here is my answer
Leaves on the ground over winter are an excellent hiding home for beasts and creepy crawlies. While the environmental side of me thinks that is great, the gardener in me doesn't like slugs, snails, Beetles and other mammals feasting on the leaves and roots of my precious plants.
Hedghogs and other hibernators need a pile of leaves or a hogitat in an area that isn't in a main border, so that they won't get disturbed.
Leaves left on borders will also start to decay down, - this isn't actually wanted as the decompostion process will take nutrients out of the soil, - so you want to collect up the leaves and put them in a pile to decompose, and then put them back on the garden when they are leaf mulch (in a year or two) and can put the goodness back into the soil as they then release nutrients
Leaves will be hiding the weeds, - this is a great time to get weeds out, as
a) there's less of them, so they are easier to spot
b) the grounds soft, so they come up easier
c) as there is little growth at the moment, the ground will look tidy for longer
So although it's hard physical work, i'll spend the rest of the month clearing leaves, so that i'm ready to start pruning in January with clean and tidy, weed free gardens.