I am trying to get a good example, but for now I will just try to give you a general description. As the Docs say this hint is used in a subquery. At compile time the optimizer has 2 options for dealing with a subquery:
1) Treat it as a black box, executing the subquery independently from the other query and then applying the results to the outer query
2) rewrite the query incorporating the subquery into the outer query as a JOIN and combining conditions from the subquery to the WHERE clause of the outer query.