Harvesting URL's is very useful when doing PPC marking on Google AdWords Content Network (placements) or Cost Per View marketing. Basically you provide the advertising networks what pages you specifically want your ad to appear on.
Obviously placing your ads on the pages (especially the first few pages) of organic search results will result in your ads being displayed to highly targeted traffic. So I put together this quick video that shows you how to do it.
Here are some pages from the video: