[kzrdude]

Aha. If one paragraph is added on page 1, it might show a diff on every following page in the same chapter after that, if it causes things to shift?

It's not easy to decide when such a change needs review and when it doesn't

[crecker]

Yes, if it causes things to shift, the tool shows every page red. This tool is meant to be ran in the final phase of typesetting, the moment when you want to focus attention on details (e.g. spacing).