Just as a general rule/tip - 'correct exposure' is a very broad term. You can have many things in your frame that is under or over 'correct' exposure, but still looks fine. Creating contrast in your lighting is often what makes things look interesting.
What I mean is, whilst you may set your aperture to T2.8, this doesn't necessarily mean you need to have every light metering at 2.8. We also test to figure out exactly the range we have, so we know where we can place lights along that scale.
For example, for a night scene, I might have the key light motivated from a prac lamp in frame. The lamp itself might be 1 1/2 stops over (i.e. metering at 4 1/2 if my aperture is set to 2.8), whereas the light falling onto the subjects face, I might want to be a 1/2 stop under (i.e. metering at 2.0 1/2 if my aperture is set to 2.8).
This is why we test to know our dynamic range - there might be parts I want to fall away to black/complete underexposure, which on a DSLR might only mean 4 stops under, but on an Alexa might mean 6 stops under.
Similarly, say the subject's house is raided by police during that night scene, I want their flashlights to be over, so that they feel 'hotter' or brighter. On an Alexa, I might be able to have them 3 stops over and still keep detail, but on a DSLR, they might blow out a face at 2 stops over, so in order to keep detail on the faces they're shining the flashlights on, I'll have to ND them to bring in them in line with the dynamic range I have.
Hopefully I'm making some sort of sense
