I have a titchy orchard area with about ten trees and I let the leaves lie there in the autumn. The soil's a bit thin and I think the worms dragging down the leaves is a good idea (and I never feed the trees and I always get good crops of apples). Excess grass clippings can do a very good job if you spread them in thin layers on your veg beds or under raspberries, but you don't want them too thick or else they'll rob your beds of nitrogen temporarily as they rot down. Excess grass clippings are also brilliant buried in heaps under your runner beans (which don't need the nitrogen anyway) as they rot into an underground mulch which conserves soil moisture (which the runner beans do need). If you leave beds empty in winter you can, if you have them, spread grass clippings over them in quite thick layers. This stops heavy rain from leaching out nutrients and wrecking the soil structure. It's a pain to dig in the mat of grass in the spring but it does the soil a power of good. Feed soil, not plants, is a good motto!