About 50 years ago when "ecology" was first being widely taught in high schools, students as far back as then learned that it was good to keep the ground covered. The covering decomposed and enriched and developed soil; it shaded soil and its multi-thousand organisms. It reduced impact of rain drops that splashed and sealed the soil surface preventing percolation into the soil layer. It reduced evaporation and allowed rainfall to percolate into the hidden depths from which good water came. Wind rows, organic strips were planted near farm houses to reduce winds and thus maintain soil and water and reduce energy costs of living in the open land. Today people know about "mulch" and its effects on soil, water runoff, and moisture conservation. Keeping the ground covered is still a good idea for all of those reasons - wind, water, climate control, erosion control, and even food and nesting places for wildlife.
The recent movement to convert wood and grass and understory plants (biomass) into ethanol did not get the ecology messages in high school and the drumbeat becoming louder ever since. We have to keep the ground covered.