It already contains the information that existed when the clone was created. If you modify one page in a large file, then only one additional page is allocated by the clone. Note that if a file is modified so that pages are appended, these pages will not appear in the clone because they were created after the clone was created. Unless you modify every page of every file in the original fileset during the life of clone, the clone fileset occupies less disk space than the original fileset. Note Changing text files with an editor may cause the entire original file to be copied to the clone.
Many editors rewrite the entire file regardless of what has changed.
When this happens, your clone fileset may grow very large. There is no way for AdvFS to alter this process. The file is not copied to the clone, but the actual delete is delayed until the clone is deleted. The version of the file that is retained is the one that existed when the clone was created. Later updates are lost.