As a gardener I have seen first hand what leaves left in the garden can do. They provide homes for the varmints who love to nest in them. While living there they are busy eating the roots of your plants, yummy!
So it is important to remove all leaves from around your plants. When the ground becomes frozen, surround the base of your tender perennials with composted cow manure. Most home improvement stores have huge clearance sales about now, so pick so up!
PS I use to rake leaves for the summer people at Lake Hayward for some extra money, I HATED the job!