Pressure is equal to the force divided by the area on which it acts. Since the smaller piston has less area so from less force also we can get more efficiency in work. And according to the Pascal's principle, in a hydraulic system, pressure exerted on a piston produces an equal increase in pressure on another piston in the system. Thus by applying little force in the smaller piston, we can get same force from larger piston too. A hydraulic machine magnifies force.
