The performance of an optical mouse is difficult to analyze because numerous parameters come into play, and the results are always a compromise. Improving one performance factor doesn't necessarily lead to a better overall result. It's a little like what happens with cars. Wider tires with thinner treads will improve handling, but comfort and road grip under difficult conditions suffer. For an optical mouse, end performance is the result of a long, complex process that includes analysis of the surface, calculation of coordinates and transmission to the computer.
Let There Be Light
A mouse's sensor takes a continuous series of "photographs" of the surface over which the mouse is moving. By comparing these pictures, the mouse's processor calculates coordinates. Obviously, for optimum measurement, the images have to be good. Thus the first task is to illuminate the surface. Until recently, red LEDs were used to do that. The surface reflects back the light, which is focused by lenses before it hits the sensor. A recent innovation by Logitech replaced the LED with a small laser. This laser creates a more concentrated beam and its light is more stable, producing a more detailed image. As in a CD or DVD player, lasers are particularly effective for detecting surface irregularities.
What an LED sees
What a laser sees