In other renderers there is Global Exposure system that affect all cameras exposures in additive way. This is very great for situation where we change lighting in scene populated with many cameras with different exposures. After that there is no need to change exposures of every camera but only Global Exposure that affect all cameras in scene.
For example. If Global Exposure in Effect was set to -2 and if you switch to camera which has exposure set to -4 in total exposure view is -6 ( -2 from Global and -4 from Camera ). So camera exposure is “added” to global exposure.
If Global exposure is -2 and camera exposure +3 in total we have final view exposure +1
That’s how it works in other renderers.