I wasn't talking about AWB, I was talking about the white point selector in FCP.
And as for the waveform, it pretty much graphs the frame on the tonal spectrum. Anything at or below 0 (labled "black") in FCP is clipped (crushed), meaning you have lost detail. The same applies to highlights being over 100.
What you should keep in mind is that just because it may technically be above the 0 mark, it can still be "crushed" in the sense that the blacks are unproportionally dark compared to the rest of the image. This is why your eyes should be the final guide.
Here's a tip: getting good contrast with an image that is predominantly white (snow with small bits of dark trees/people) isn't achieved by dropping the blacks (sharp contrast between black/white), so ease up on the black slider! If you want good snow contrast, drop the mids, and raise the whites. Then adjust the blacks to fine-tune dark stuff. This way you can get plenty of dark detail and snow contrast simultaneously.