there should be two kinds of update:`full update` and `quick update`.
in full update, check all links.
in quick update, only check links in updated links.
If index.htm is the first page. When index.htm have no changes, other files in the site normally do not change. If one inside file is changed, the webmaster will say it on the first page.
So, we dont need to check all links.
That`s not always true. When the index page contains a table of contents or article titles linked to topics, the topics are often updated but not the table of contents or the index.
Both of these issues can be easily solved in Offline Explorer. There is a special mode "Skip existing files on levels higher than...". It means that Offline Explorer will download the first page and then it will only download missing files (that were added to the index page recently). If you set level to 1 there, it will be the index page, links from it and then only new files on other levels.