Introduction:
In a common-source (CS) amplifier or a common-emitter (CE) amplifier, the addition of a small resistance in the source or emitter circuit can significantly improve the performance of the amplifier. This resistance is commonly referred to as source/emitter degeneration or emitter resistance.

Explanation:

1. Bandwidth increases:
- The addition of a small resistance in the source/emitter circuit increases the effective resistance seen by the input signal.
- This increased resistance reduces the overall gain of the amplifier.
- However, it also improves the stability and linearity of the amplifier.
- As a result, the bandwidth of the amplifier increases, allowing it to handle a wider range of frequencies.

2. Voltage gain increases:
- The small resistance in the source/emitter circuit helps in stabilizing the amplifier by reducing the gain.
- The gain of an amplifier is inversely proportional to the resistance in the source/emitter circuit.
- By increasing the resistance, the gain decreases, and the amplifier becomes more stable.
- However, this increase in resistance also helps in improving the voltage gain of the amplifier.
- The increased resistance reduces the effect of load resistance and improves the voltage gain.

3. Input resistance decreases:
- The addition of a small resistance in the source/emitter circuit significantly increases the input resistance of the amplifier.
- This increased input resistance helps in reducing the loading effect on the input signal.
- However, it also reduces the overall input resistance of the amplifier.
- The reduction in input resistance can be beneficial in certain applications where a lower input resistance is required.

4. Output resistance increases:
- The addition of a small resistance in the source/emitter circuit also increases the output resistance of the amplifier.
- This increased output resistance helps in reducing the loading effect on the output signal.
- However, it also reduces the overall output resistance of the amplifier.
- The increase in output resistance can be beneficial in certain applications where a higher output resistance is required.

Conclusion:
In conclusion, the addition of a small resistance in the source/emitter circuit of a CS/CE amplifier provides the designer with a tool to improve the performance of the amplifier. It increases the bandwidth, improves the voltage gain, decreases the input resistance, and increases the output resistance. However, the designer needs to carefully consider the trade-offs and select the appropriate value of resistance based on the specific requirements of the application.