Why wouldn't you want to rush the process of breaking down leaves? That's what compost is: a rushed decomposition process. Your chipper/shredder is an awesome tool for composting. Save your grass clippings throughout the summer. Add grass clippings to your leaves in the fall as you run them through the shredder. If you get the moisture right, you'll get hot compost. Conversely, if you save some shredded leaves over the winter, add them to fresh grass clippings in the spring and run the mix through the shredder. This will work even better.
In my experience, mulching, or covering the soil of the annual garden isn't really desirable. It seems to create habitat for pests, and I don't really see the benefit. I don't want the soil insulated in the spring because where I live the frost would stay in the ground until June if it was covered with dry leaves. Covering perennials with leaves over the winter is great though. You'd want your shredded leaves to be on the dry side, and not too fine, because I think the covered plants still need to breathe a little bit.
