Cutting your lawn too short, or scalping, will damage the root system of the grass. Scalping happens when two-thirds of the leaf blade is removed and the stem is left standing. Studies show that by cutting your grass high, the roots grow deeper, allowing them to take in more moisture and nutrients. As a result, the grass grows thicker.
Experts caution against removing more than the top third of the grass blade. A taller lawn will not only blossom better than a shorter lawn, but it also will cut down on the number of weeds. Taller grass also shades the soil, which means the roots won't dry out as fast [source: Dream Yard].