Pumps with a specific speed value below 6000, when primed and operated at full speed with discharge valve closed, require much less power input than when operated with the valve open.
For this reason, it is advantantageous to close or nearly close the discharge valve when the pump is  being started.
After start-up, prolonged operation at shut-off is harmful and should be avoided because of:
Increased vibration levels affect the bearings and shaft seals     Increased radial thrust and resultant stresses in the shaft and bearings     Heat build-up resulting in dangerous temperature rise of the liquid being pumped     Excessive cavitation damage resulting from internal recirculation
When shutting down, the discharge valve is usually closed first. If the discharge piping includes a check valve, no other valve closure is necessary.