If sensors had infinite dynamic range, then one would never need to set exposure
at all in the camera -- just fix it in post procssing.

But sensors do not have unlimited dynamic range. And the number of stops that
can be encountered in nature is unlimited. Imagine yourself trying to photograph
sunspots. Or the sun rising over a train tunnel. Or just bright snow and shadows on a
sunny winter's day. And once detail has been lost from a blown highlight, there
is no getting it back. (Shadows that look pure black to the naked eye aren't and detail
can be recovered in processing, but not blown highlights..)

In a very contrasty situation, you are going to lose detail in either the shadows, highlights,
or a bit of both. If you leave it up thte camea, you'll get the latter. But that doesn't
necessary look the best.

Shadows that appear pure black sometimess aren't, and the detail can
be restored in processing. But blown highlights are gone forever.

Dialing in 1.5 stops of additional exposure (over what the meter calculates) is
asking for blown highlights. But of course, it depends on what and where one
phtographs.

What's a "seasoned pro" -- some guy who takes passport photos? Or school pictures?

The statement "+1.5 exposure comp because that's where white sits on the spectrum"
makes no sense at all. White isn't in the spectrum--it's a mixture of spectral colors
(according to some guy named Isaac Newton--but then, he wasn't a "seasoned pro").

But there's a another reason not to ignore exposure and then try to fix it in post-processing:
you may not remember how the original scene looked. For example, in a portrait, you
may have forgotten exactly how light or dark the sitter's complexion was. Whatever it
actually was, in a close up autoexposure will give him an olive complexion (middle tone).

That's how autoexposure works: it takes whatever it meters (average, center-weighted, spot,
matrix or whatever), and adjusts the exposure so it's portrayed as middle gray (or some middle tone).
What else can it do? It doesn't know what it's looking at, or what tone anything actually is. It just
see patterns of light, and applies an algorithm.

Lots of people let their camera chose the exposure -- they just leave it in Program Mode.
Most of the time, that sort of works, provided you're not too particular and are willing to try to
patch it up in post processing.

But the reason one hires a photographer is to get a photographer, not just a camera. If that person
waits until post-processing to try to fix exposure, he's taking a big risk. The event or wedding is
over, no opportunity to try again.

Most camera users today don't make prints and just display images files once or twice on a small,
low-contrast LCD/LED computer monitor. If that's the "final image" then why not leave the camera
in Program Mode, leave it in autofocus, and leave the same zoom lens mounted all the time? No need
for full frame, let along anything larger. And why even bother to keep the lens clean--nobody will
notice a few fingerprints.

I find this extremely depressing.