>>2992573there's three parts of exposure.
Aperture, Shutter, ISO.
In lightroom or any editing, you can't affect aperture or shutter at all. Essentially you'd just be using an even-more-shitty ISO change to brighten/darken.
If your body is ISO-6400 when it could've been a lot lower, then you darken the scene on your computer to Resemble ISO-1200 or whatever, it will retain all the ugly noise from 6400, it will be darker but the image will have an ugly digital grain dispersed randomly.
It's like turning a photo into a JPEG, it's a process that cannot be reversed at a computer. The information is gone before you even start to process it.
Doing compensation in body when appropriate will mix several of the three parts of the exposure triangle (aperture size, shutter speed, image sensor sensitivity) so that one part doesn't dominate.
If the camera over-manipulated your aperture, you'd miss focus (wide open) or get bad diffraction (closed tight)
If it over-manipulates just the shutter, then you'll either get completely blurred moving objects or you might have wanted a very gentle blur and instead you'll have absolutely zero motion.
Also, half of the flash lighting systems don't work at extreme speeds like beyond 1/250 sec, which is why darkening with only shutter can be problematic.
And if it over-manipulates ISO alone, all that noise is either hideous or all detail is lost after using heavy noise-reduction (textures, colors and lines end up mooshed together and out of focus)
It's far better to adjust 2 or 3 simultaneously, like at aperture 16 you've darkened things without the diffraction of 22. While at shutter 1/250 you can still use a basic flash. And a moderate iso like 600-800 should have effect without being noticeable in most print sizes or web sizes of image without extreme zooming.
My body re-uses a different wheel for comp, but it's smart enough to blend multiple settings in stages.
Like iso-change, iso-change, shutter-change, aperture-change, iso...
