Pages detected to have identical contents are replaced with a single read-only copy, consequently reducing the amount of host memory used. If an identical page is written to, it will again get a private writable instance of the page.
Identical pages are detected during run-time by certain triggers. If the -now switch is used, all currently active pages will be examined for sharing directly. Disabling page-sharing only means that no more pages will be shared, pages which have already been shared will not be un-shared.