HI Julie, I think you can do both. Leave most of the leaves around the base of your tree and shrubs but rake up the leaves that make the area look messy. I like to fill plastic garbage bags with leaves then poke holes in the bag for air and add a shovelful of soil to the leaves. Then I store these bags of leaves over the winter. In spring I have leaf mold to use as a more tidy mulch around plants.  To cut back on slugs and disease just remove any heavy layers of leaves in the spring so that the trunks and crowns of shrubs have air and sunlight. During the winter the leaves help to insulate the plants from cold. If you have a huge tree you will not be able to use all the leaves in the same area so you may want to rake, then move them to other beds. As long as you don't have lawn you can have leaves on the ground in the winter. Hope this helps, Keep growing, Marianne Binetti