Pumps are not 100% efficient. A pump converts kinetic energy to pressure energy, but some of the kinetic energy is lost before it can be converted. These losses can occur either internally or externally. Examples of internal loss include hydraulic losses through friction from the impeller, losses due to changes in flow direction and velocities throughout the pump and volumetric losses from internal recirculation due to wearing’s or bushings. External losses are usually mechanical in nature due to friction in the seals and bearings.
The Best Efficiency Point (BEP) shows where the pump is performing most efficiently. A pump should operate near its BEP and this point should be provided by your pump manufacturer. Pumps can be operated at other points on the pump curve, but will have lower efficiency.
A good system design would to have every pump operating at the BEP.
Pump manufacturers are continually developing the design of pumps to improve the efficiency.