What is the effect of proportional gain on system response?

Increasing proportional gain (Kp) reduces rise time and steady-state error but increases overshoot and may cause instability if too high. Proportional control alone cannot eliminate steady-state error in Type 0 systems - some error is always needed to generate the control effort. The closed-loop response with P control is: steady-state error = 1/(1 + Kp*G(0)). Very high Kp makes the system respond quickly but oscillate excessively; too low makes it sluggish.