What is the use of flash chamber in a vapour compression refrigeration cycle to improve the COP of refrigeration cycle ?

When liquid refrigerant as obtained from condenser is throttled, there are some vapours. These vapours if carried through the evaporator will not contribute to refrigerating effect. Using a flash chamber at some intermediate pressure, the flash vapour at this pressure can be bled off and fed back to the compression process. The throttling process is then carried out in 2 stages. Similarly compression process is also done in two separate compressor stages.