However, you can use the secondary CC to make your green screen even more green and help achieve a better separation between subject and screen.
Apply secondary CC.
Click on the eyedropper and select a bit of the screen.
Check Mask only and adjust to get it right.
Uncheck Mask only and pump up the saturation.
Apply the chromakey FX.
I sometimes use the Secondary Color Corrector as primary keyer. It works a bit different as the Chroma Keyer, one of its advantages are more control and - this is why sometimes I love using the Secondary Color Corrector for keying - you can use it in a cascading way (this does not work with the regular Chroma Keyer). The key is to set the value of Alpha to zero in the end.
And sometimes it is worth combining the two different keyers - first applying one (or some cascading) chroma key using the Secondary Color Corrector and then applying another chroma key using Chroma Key.
If one of them does not work fine - maybe the other one will do the job. And if this doesn't help either you will be fine combining them.