Look at it this way:
you have an image which ‘as is’ has the highlights (say clouds in a landscape) just right. So nothing to do in filmic, but modifying contrast and black point.
But the foreground (for one reason or another) is way to dark, so you want to apply 1EV extra exposure. No problem, except that now you have to go back to the filmic module to correct your highlight, which also got that extra 1EV, and are now overexposed…