Hi
if you look at the range of exposure in my histograms on the first part of
this page I think it answers some of your questions. Essentially its nice to know what and where the histogram for clear film base is and what is the densest you can get with your negative.
This will then let you know when you scan it if you have a good density range or contrast range in your exposure.
From then I usually invert and then make the curves dependent on the image / scene contrast range. I recently cross checked this with some prints done at different grades of filter ... sadly I didn't get around to writing this up yet ... and wonder if any are interested anyway ;-)