The latest update to the web advertising platform, DoubleClick for Publishers (DFP) API, introduces SuggestedAdUnitService, which simplifies the process of getting and approving capable ad spaces on your website (but no corresponding ad units in DFP). The new feature will return ad spaces that receive 10 or more requests as suggested ad units, which can then be approved with the API action performSuggestedAdUnitAction. These capabilities require a premium account and require enabling in the user interface.
Google gave the example of a publisher or blog owner creating new tags for articles and posts within their website, and then approving the units based on the number of impressions, once the article picks up steam and gains better traffic. Essentially this feature gives you line item targeting while having the ad spots in place and ready to go.