Lowering the weight of bike parts, sprung or otherwise, will have advantages in terms of acceleration – thrust divided by weight equals acceleration. This will add power and/or reduce the weight of the bike and therefore the bike will be faster. When you eliminate 3kg from a 100bhp, 200kg bike it is roughly equal to gaining one extra horsepower. 

For example, if you reduce the weight of a wheel, it will have even more effect on acceleration, as power is used in acceleration of the rotation of a wheel (along with tires, sprockets, discs) itself. Any weight saved on these rotating parts, means less power used in spinning them up to speed and a consequent increase in the power left to accelerate the mass of the entire bike. As a direct, result, weight lost from the wheels or rotors, will be directly felt by the rider.