For measurement of potential difference, potentiometer is preferred in comparison to voltmeter because
(1) Potentiometer is more sensitive than voltmeter
(2) The resistance of potentiometer is less than voltmeter
(3) Potentiometer is cheaper than voltmeter
(4) Potentiometer does not take current from the circuit
(4) Potentiometer works on null deflection method. In balance condition no current flows in secondary circuit.