As previously stated, the electrical power consumed by the pump, is usually lower while using a CSV.
To clarify, without a CSV, pressure to faucets will be either dropping from 60 psi down to 40 whereby the pump will become activated, then the pressure will rise again.
Once the pump is running, it will be pushing out maximum flow, so if not all of that water is being consumed, such as while running a 2.5 GPM shower head, then the pump's additional GPM capacity will flow to the pressure tank. Once the pressure rises to 60 PSI, the pressure switch will shut off the pump, which will cause the system pressure to begin to drop again, and the cycle will continue for as long as water continues to be consumed.
Starting the pump each time will result in additional electrical load being briefly placed on the system, which will result in greater heat within the pump motor from the higher current draw during each startup. Repeated Starts/Stops within short time periods, will cause significantly greater heat buildup in the motor, and without sufficient run time to cause cooling water to flow over the motor, the motor is more likely to overheat.
With a CSV, because a CSV only controls the flow rate from the pump, the initial pressure to faucets will become lower until the pump becomes activated, then the pump will continue to run and the pressure from the CSV will remain constant for as long as >1 GPM continues to be consumed, regardless of whether that is 5-minutes, 5-hours, 5-days, 5-weeks or 5-years.
Because a CSV will vary the flow rate from the pump to equal the rate of flow being consumed, the pump will typically need to move less GPM than it's capable of doing, which will reduce the pump's workload, which will usually reduce the power consumed and the amount of heat generated. With fewer Start cycles, there will be less additional electricity consumed for startups, and the longer run times will continue to draw cold water over the pump's electric motor.