For normal operation, base-emitter junction should be forward biased and the collector-base junction reverse biased. The amount of bias required is significant for the establishment of the operating or the Q-point which is dictated by the mode of operation desired.
In case the transistor is not biased properly, it would :
- work inefficiently
- produce distortion in the output signal
- with the change in transistor parameters or temperature rise, the operating point may shift and the amplifier output will be unstable.