Multiple Fetches allows a page to be fetched multiple times,
and can potentially slow down a walk. It should only be used in
specific situations in conjunction with Off-Site Pages.
For example, Consider the situation of walking two sites, a.com
and b.com with Off-Site Pages enabled. A link from a
page on a.com to b.com/page.htm is considered off-site,
so it will be walked but its links won't. Then, when b.com
starts its walk, b.com/page.htm won't be processed because
it has already been done, causing b.com/page.htm's links to not
be included.
Multiple Fetches allows the 2nd encounter of
b.com/page.htm to be processed again, which will allow its
links to be properly processed.