I see, like deconstructing a, for example, black forest cake. You might need those cherries to make some other fruit so you take them out of or off of the cake and put them to some other use.
Interesting!
Well, I guess if you'd cooked more than you need you could just uncook it to get the raw ingredients back so they could be reused? Only a portion of the ingredients, of course.
And by round file, you mean of course donating, which also gets you other valuable things, like IMG and favor and such.
I can see it being useful if, for example, you only have 25 beans, not 30, and have a hankering for chili while off in the depths of, say, somewhere that totally lacks beans. I don't think it's necessarily a vital skill, but I suppose I can see where it would appeal to some.