DD Diva, you nailed it:
unless you're tracking the changes for digestive medical purposes
. This is exactly why I do an evening and a morning weigh in! So don't worry, I don't compare evening and morning figures for weightloss (fat loss) ...that would truely be demoralising - and, as you say Blitz, inaccurate!
I compare morning with morning, and evening with evening, for TRENDS to indicate fatloss. Then I also look at those comparisons for medical understanding, plus the evening to morning comparison. My dietician explained lots of processes (when things malfunction) for me, and it can be useful info for them to see what predominant reactions my body is having. It isn't a 'food content' weight I am at all concerned about - it is how my body responds to certain foods, meds, and exercise situations, and how that may lead to clues for new health approaches. I am apparently intolerant to certain carbohydrates and sugars (in many grains, fruits, and veges)- and people can react in two main ways...one which will show in increased weight (among other symptoms) irrelevant to food intake/weight of food (and it also is why I have to drink H2O so much in comparison to 'normal' people). So the PM/AM tracking is very informative, medically, and I'm still getting to understand my body.
On a more interesting note, I was also able to get some help with feeling terrible after dancing for 2-3hrs at night, from this weight tracking. I was really surprised that the evening weigh-in after I come home from intense exercise was not low - it is consistently higher than my 'current -(whatever it is)' evening measurement by 2 kilos. You'd think I'd be lighter from all the sweat, ie, there'd be water loss. The dietician said it was actually water weight...from all the water I drink! I'm not actually absorbing it properly (and this apparently happens for people who do intense exercise for over 1 hr). Hence why I run a tendency for migraine and pain episodes after dancing for more than 1 hr...Her solution was a sports drink for the electrolytes as I need to get properly hydrated. Unfortunately, I didn't get a chance to test this hypothesis out, as shortly after this I was put on an allergy diet - no sports drinks permitted. But it was incredibly interesting, and something I will try out soon now that I'm weaning off that horrid diet (and when I actually feel well enough to go out and dance like that for pleasure).