In these systems, the platform is attached to a hydraulic ram. To move the lift up and down, hydraulic fluid is pushed into or removed from the ram via a pump from a central reservoir, causing it to extend or contract as necessary.
The drawback of hydraulic drive systems is that the pump and reservoir takes up a huge amount of space, often beneath the lift, meaning where space is at a premium the hydraulic drive system might not be appropriate.
They are also quite noisy in comparison to Screw and Nut Drive systems, and the cables generally need replacing every 5 or so years due to stretching.
In hot weather, the hydraulic fluid can also sometimes give off an odour, and will need to be drained and cleaned/changed at points.