I think I understand this function, but not so much the purpose of it.

Trying to think about some scenarios where this functionality would be purposeful.
(if you have some I am not aware of, please let me know)

1. to have a glance on the final work without the unwanted 'leftovers'. InDesign has a nice 'print view' quasi-mode, like Joshua mentioned. One keystroke (W) hides all the guides, hides everything outside the page, shows only what will be printed. Click W again, you're back 'in the workshop'. Is something like that what you had in mind?
2. a quick finalizing cleanup. In that case, a selection script would maybe be more appropriate, I think.

In both cases, I have a feeling that a function like that would not be a good candidate for a 'tool'.
Moreover, If I have understood correctly the discussion above, I have some practical questions:

About the page resizing...
What would be the practical purpose of having a page scaled to fit the graphics? (why not the other way around?)
How is a resulting page used in the workflow? (it would be a non-standard page in most cases, right?)
How would we define the parameters for the generated page? (would there be bleed, inset, outset, margins, ...?)

About the cropping...
The need for this aspect is clearer to me. Especially if it allows the user to use any of the path editing/creating tools to define the crop.
Is there a way to achieve the same purpose without being destructive? (the artists often go back and forth in their workflow)

Alex