With negative feedback, the system stability and system gain respectively

Effect of negative feedback system:

• Negative feedback in a control system reduces the overall gain and increases stability.
• It reduces the sensitivity of output to input variation, distortion, and noise reduction.
• It improves bandwidth and input and output impedances (reducing impedance and increasing bandwidth which are desired in most cases)

Important Points

Positive feedback:

In open-loop system, we do not have any feedback path but in closed-loop system, we have a feedback path.

The transfer function of closed-loop transfer function, with positive feedback, is given by \(\frac{{G\left( s \right)H\left( s \right)}}{{1 - G\left( s \right)H\left( s \right)}}\)

The overall gain of the transfer function increases with positive feedback. 

Negative feedback:

The transfer function of closed loop transfer function, with negative feedback, is given \(\frac{{G\left( s \right)H\left( s \right)}}{{1 + G\left( s \right)H\left( s \right)}}\)

The overall gain of the transfer function decreases with negative feedback.