The bitrate of your plan determines two things:
The bandwidth used to stream to the SHOUTcast server, and the bandwidth used to listen.
For most places, this bandwidth used is trivial. Listening on devices with low bandwidth may experience problems buffering audio at higher bitrates. The official SHOUTcast iPhone app filters out 128kbps stations by default as it determines that most 3G connections aren’t fast enough to listen without interruptions.
The quality of audio
The lower the bitrate, the less data that is sent to the listener and the lower quality of audio received. At lower bitrates, music will lose its fidelity and start to sound distorted. As an example, we have encoded a piece of music to each of the bitrates we offer. We’ve encoded the music in MP3 format as it’s by far the most commonly used format.