Why is it beneficial to use satellite launch vehicles made of more than on stage ?

Explanation

Earlier Satellite Launch Vehicles (SLV) used to be of a single stage vehicles. Such SLV's used to be vary heavy as well as expendsive in terms of its fuel consumption. As a result, SLV's with multiple stages were developed .
In multistage SLV's as the journey of the launch vehical progresses and the vehicle achieves a specific and a certain height , the fuel to the first stage is exhausted and the empty fuel tank gets detached from the main body of the launch vehicle and falls back into a sea or on unpopulated land. AS the fuel in the first stage is exhausted the engine in the second stage is ignited. However, the weight of the launch vehicle is now less than what is was earlier and hence it can move with higher velocity.Thus, it saves fuel consumption. Hence, it is beneficial to use a multistage satellite launch vehicle.