One of the additional benefits of longer grass is the improvement in color. The lawn becomes more consistently lush looking when the grass is longer. Longer blades of grass provide more area of photosynthesis to occur, which both strengthens the roots and allows for plant growth.
You can see this difference from the picture on the right. Both of these lawns have received the same amount of watering and fertilizing this year (none other than what mother nature has provided). The lawn to the right is cut at 3 1/2 inches, the lawn on the left much shorter. The lawn on the right also has benefited by use of a mulching mower, which leaves the grass clippings on the ground.
It only takes a few moments to change your lawn mower's height. If you haven't already made the adjustment I would encourage you to do it now. Your lawn will thank you!