Makes the pressure setting itself variable. Instead of being set by hand to one value, it takes an electrical signal and adjusts its setting continuously while the machine runs, so pressure becomes something the control system commands rather than a fixed property of the circuit.

Recipe-driven clamping force, presses applying different pressures at different points in a cycle, test rigs ramping through a pressure profile, and machines changing settings between product batches without anyone adjusting the hydraulics manually. All of it without a spanner. None of it requires anyone to touch the hydraulics with a spanner.

Yes - pressure can be reduced automatically whenever full force is not required, which cuts both energy consumption and the heat that has to be rejected. On a duty cycle with long periods at partial force that saving is continuous rather than occasional.

The same distinction as their conventional counterparts. A relief valve limits maximum system pressure to the commanded value; a reducing valve holds a commanded pressure in one branch below system pressure. Which you need depends on whether you are capping the system or setting a sub-circuit.

Open loop, it depends on the valve's characteristic and the amplifier calibration, and there is some hysteresis. A closed-loop arrangement with a pressure transmitter feeding back removes that uncertainty and is what should be used where the pressure value genuinely matters.

It can contribute - dropping to a safe pressure during setup or when a guard opens is a real benefit over relying on procedure. Whether it is acceptable as a safety function in its own right depends on the machinery safety assessment, and a proportional valve alone rarely satisfies a high safety integrity requirement.

Yes. It is a proportional component with the same fine internal clearances and pilot passages, so the stated cleanliness code applies. Contamination shows up as a commanded pressure that is not achieved or that drifts, which is easily mistaken for a calibration problem.