Explain the advantages and disadvantages of rheostat?

A rheostat is an electrical component that has an adjustable resistance. Rheostat is helpful in obtaining varying current in the circuit by changing the value of resistance. For example, a rheostat is used to change the brightness of a bulb by connecting it in series.  When the resistor has a high resistance the bulb is dim. When the resistance is low the bulb is bright.
But in some cases, rheostat doesn't give satisfactory results. ​For example, a rheostat lowers the voltage supplied to the fan motor.  This causes the motor to overheat and destroying the motor.