Unless you have a very heavy layer of leaves, they won't smother your lawn. Most lawns are going dormant by the time leaves start to fall, so the myth that leaves will kill grass is false. Leaves biodegrade, of course, and they'll decompose by the spring.

Should leaves be left on lawn over winter?

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. And finally, turf damage from critters (voles, mice) can be more extensive in the spring.

Is leaving leaves on your lawn during fall good?

When the leaves break down where they fall, they return essential nutrients to the grass and soil. Additionally, the coverage that the leaves provide preserves soil moisture and suppresses weeds. Finally, birds and insects such as butterflies and moths depend on the fallen leaves.