Native camera data is linear but our eyes see things differently.
Luminous Landscape has a nice page on 'expose right' which explains this
clearly. If you want to be very technical about making adjustments, like
in scientific or astrophotography it can be cleaner to work with the
original linear data rather than stretching it all up & introducing
rounding errors and clipping and exceeding the bit depth of the
software. I only have a vague understanding.

A linear image is one where double the pixel value doubles the light
level.

Your monitor is set up for a non-linear space, when you put a linear
image on it the mid tones end up much darker then in reality.

If you want the unprocessed output from a scanner it will be a linear
image.

Scott