When designing a social network that depends on users to contribute content from which they'll collectively derive value, one must consider certain qualities of its supported content types to determine whether those types can provide enough ongoing value to keep users engaged.
Among these important qualities is the frequency with which people are compelled to create and share a given type of content. People are interested in sharing some types on a seemingly continual basis, spacing out contributions mere hours, minutes or even seconds apart. Conversely, there are types that make sense to share only occasionally when unique opportunities or needs arise.
While the suitable frequency of each type varies between individuals, generalizations can be made for evaluation and comparison purposes. For example, status updates, which a given person might find him or herself compelled to produce several times per day, lend themselves to a greater frequency than blog posts, which the same person might publish only every few weeks.
The general frequency of a particular content type results from numerous factors that affect the costs and benefits of sharing it. All else being equal, types that are easy to produce, such as check-ins or one-off photos, enjoy a greater frequency than those that take more time and consideration, such as restaurant reviews or entire photo albums. Types that return more value to the producer, such a thoughtful answer to a question that earns social acclaim, also enjoy greater frequency than less beneficial types that require the same investment.
It also seems clear that people, due to their impatience, have a greater cost elasticity than benefit elasticity, in that a little less effort makes a bigger positive impact on frequency than a little more benefit. This asymmetry might help to explain why we've seen smaller, bite-sized types of sharing emerge, whereas we haven't seen as many new services that target types with higher costs yet higher yields.
It's also possible that with current feedback mechanisms (which provide superficial doses of social validation rather than more impactful, long-standing personal gains), there are simply more apparent opportunities to reduce costs than increase benefits, even if that results in a downward movement of publisher value (and likely consumer value) per share.
Every type of content has its own set of reasons for why it presents people with higher or lower costs and benefits, and a study of each is necessary to understand their resulting frequencies. When choosing one or more types for a new service, it's important to conduct this study to determine whether they'd yield a high enough frequency to engage users on a continual basis.
Higher frequency generally leads to greater engagement if only because it enables the production of more content within a given period of time and, after all, content is the lifeblood of any social network and needs to accrue. If the value of content is also dependent at least partly on its recency (as is the case with virtually all types, to varying degrees), frequency is even more important because there must be enough new content available at any given time that users decide to engage with the service. The depreciation of existing content essentially needs to be counteracted by fresh content at a sufficient enough rate.
The need for a relatively high sharing frequency is particularly acute due to an increasing number of services vying for consumers time and attention. Each additional service drives up the minimum value users demand from the next, either as producers or consumers of content. An important question for social network designers, then, is what are the types of content that will provide enough net publishing value that they elicit frequent contributions from their target demographics, especially as their opportunity costs rise.