Role of Performance Factor in EVM:
Performance Factor (PF) plays an important role in forecasting while calculating the value of Estimate to Complete (ETC) in Earned Value Management (EVM).
Different values of this Performance Factor will generate a totally different value of ETC, which in turn would help in the calculation of the Estimate at Completion (EAC).
In fact, Earned Value Management (EVM) method already has a simple option to calculate the value of ETC by taking the value of Budget at Completion (BAC) and Actual Cost (AC). But this option will not work in most conditions. Definitely, there will be situations when CPI and SPI are not equal to one (1), which means this simple method will not generate a correct value of ETC.
for more info Please see the Following link