In general, heat pump needs to match Evaporator Coil size.
For Example, a 3-tons heat pump must match a 3-tons Evaporator Coil!!!
In a Heat Pump slit system, heat pumps should definitely match the coils, because in the reverse-cycle mode the internal volume and heat transfer characteristics are critical. Refrigerant flood back to the compressor, high-pressure lockouts due to undersized indoor coils, and problems due to differences in check valves on the indoor coils are all potential problems.
However, the straight Air Conditioner (AC) systems do not need to. In AC system, the compressor can be 0.5 ton smaller than Evaporator Coil so it will slightly increase its efficiency!
For example, a 3-tons Air Conditioner can have a 3.5 tons Evaporator Coil.
However, Increasing the size of the evaporator coil in an Air Conditioning system will cause a less ability to dehumidify - That means the metal ductwork of HVAC system could be rusted quickly than usual!!!