Machines at work have pressure on one side or the other all the time, you are either forward or retract. It has a pressure regulator to keep pressure constant. Only time pressure is off is when power is dropped then it goes to vent. (no pressure). Older power steering systems have pressure on one side or the other all the time the motor is running. Some of the newer systems have oil over air for pressure , More precise.

Just my two cents, it seems that a hydraulic system should be cycled or pressurized once during a system start up. I think this would help the seals from drying out.