It makes sense when you're browsing (consuming, syncing, mashing up) your own stuff that you want access to an organized1 mass of it. You're essentially the curator and your audience is you + other who you will decide to give access to some or all of it. However when other people are added as an audience, it's not clear whether you should send them a message with some of the stuff (the ones you have selected or curated) or give them a link that points back to the source of the data so they can make their own decisions on what is compelling. Traditionally the distinction between the 2 modes of third party consumption are messaging and sharing.
Messaging is great for spontaneously making stuff available to an audience, especially in manageable doses (limitation or a feature?). It's also well suited for form factors that transcend the PC, like phones. What is missing from messaging is extended discovery; being able to step beyond the curator (you) to get to interesting stuff that matches the long tail of consumer individuality in consumption. On the other hand with sharing, sometimes the inundation of information is pretty overwhelming or pretty irrelevant. Curators exist for a reason.
Some axes to determine efficiency: a) bandwidth consumed b) long tail satisfaction (or discovery) c) satisfactoriness of the information proffered in context of interest in the information proffered d)effort of the curator, including repetition.
I suppose the most efficient model I have seen is mating sharing with a social graph so that messaging is accomplished implicitly instead of explicitly (basically all my contacts get notified if I upload pictures, I don't have to send an email), and discovery is also possible since all the available information is up for perusal. If that's true then messaging is losing out. Watch out email, mms and sms J.
1 Data organization is hard. The music devices and software have it right – use the metadata to pre-organize for consumers. If they want to layer their own taxonomy on top of that, fine…