Excessive leaf matter on your lawn going into winter is bad for several reasons. First, it will smother the grass and if not removed very soon in the spring it will inhibit growth. Second, it can promote the snow mold diseases.
In Maryland, we primarily have cool season grasses that will not survive if choked for long periods of time. Stay on top of maintenance, we recommend two sessions. Once the majority of leaves fall in mid/late October, and again in early December before the frost sets in. If you've missed the optimal dates, do not worry. It is better to remove them now than to wait to spring.