That's a good point you raise. Being able to light a scene preemptively. If you're lighting within your cameras latitude however wouldn't the contrast ratios stay the same anyway? Or at least be very close.
Sometimes you'll have different types of camera, in this case something like the Sekonic 758, for example, allows you to store multiple dynamic range profiles for different cameras to ensure consistency.
The consensus seems to be that lighting before cameras arrive can be more easily achieved using a good light meter.
Also, in a situation where on-set monitoring is not of the highest quality, one might benefit from the second opinion of a light meter so as to be sure of no nasty surprises in post..
Though good WYSIWYG monitoring and the decent (if not always film-like) latitude of modern digital inspires us with a lot of confidence that things can be rescued in post, total consistency can be achieved by checking the light in reality, so to speak.
Thinking about it, metering is not so useful (in the rawest sense) with Red, Alexa or F65 as the latitude is enormous, and preview monitors using a higher contrast profile can be used to show a rough final result.
However, when recording to a lower dynamic range 4:2:0 8 bit profile, it's arguable that many would benefit from using such metering on set, it's often the case that protecting the highlights from digital clipping will crush the blacks, and It's probably easier to have a meter tell you the range of a scene and how much fill light is appropriate, than it is to guess with the WYSIWYG.
