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Following are three specific circumstances in which advertising a resource widely may make sense. In all cases, terms negotiation becomes a key "line of defense" for authorizing access; see the scenarios specific to terms negotiation later in this document for more detail.
Sharing Exclusively with Family and Friends
Authorizing user Roxy wants to share her blog posts and song recordings only with family and friends. She publishes her posts and songs in feeds that are accessible only to those who can prove they are her family and friends, as she knows them through interactions on Twitter and Facebook and other social sites. (See the Requester Identification terms negotiation scenario to see details on how this access control scenario might work.) She also requires requesters to agree not to share this material further.
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In this case, each of her loved ones is a requesting party, working through some requester intermediary (such as Google Reader or Songbird) that helps them access her protected resources, which hosted either on her blog or elsewhere.
Sharing
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Resources on a Commercial
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Basis
Roxy Authorizing user Selma is also an accomplished photographer, and she offers her photographs at full resolution for sale to any requester who can produce a receipt for US$10. The photographs are available at low resolution on the site, with the URLs of the full-size photographs advertised. When a potential photo purchaser tries to "hit" a full-size photo, they are told of the requirement for successfully getting the photo and given the opportunity to comply.
Sharing
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Personal Requests for Proposals (PRFPs)
When authorizing user Dirk's coffee maker dies, she he constructs an online " personal RFP " (a description of her his parameters and constraints for an acceptable replacement coffee maker, including height, capacity, basket style, price, and so on), hosted at a site that specializes in PRFPs that she he has already registered with her his AM.
One of the host site's services is to get her his PRFP seen by various online retailers, and she he might also tweet the PRFP. The online retailers will need to register with her his AM as requesters in order to both see the PRFP and to supply a coffee maker proposal in a special inbox also hosted by the same site. Each proposal could contain an "offer URL" that allows Roxy Dirk to take advantage of each deal directly on their site, or could give other instructions on how Roxy he can get the deal.
Preventing Denial-of-Service Attacks on a Resource
Authorizing user Reed has a popular documentary blog where he exposes corruption and budgetary malfeasance in his home state, which he is happy for anyone to visit. However, the subject of his writing has made him collect some high-powered enemies. Some of them want to try to shut him down by flooding his blog and his comment threads with Denial-of-Service attacks. So Reed configures his AM to require that all requesters "prove their sincerity", in effect, by performing proof of work.