I rake the leaves off the grass so it grows in the summer. Grass is much better than dirt for keeping a yard cool in summer.

I do rake leaves under the hedges I've planted on 3 sides of our yard (obviously the house is on the 4th side). This keeps the natural nutrient cycle working and gives critters a place to nest.

There is a reason for clearing leaves off of bike and hike paths just like terraces: rotting leaves are slippery as hell if they are even a little wet.