In this context, it would make sense to remember the NOPES model. The sharing of information happens between persons (individuals, organizations). When we are writing a blog or a diary, this blog or diary entry can fall into the five main categories, really:
[N] - for Names -- a post about a person or organization.
[O] - for Objects -- a post about a physical object.
[P] - for Places -- a post about a location (geographical, spatial locations, where N, O can be found)
[E] - for Events -- a post about a spatio-temporal event, e.g., a supernova explosion, a new discovery, e.g., an olympics, a vacation.
[S] - for Subjects -- a post about a problem, idea, e.g., idea how to find a friend, organize information, treat illness, an algorithm, a methodology, a thing to try/experiment, a formula, etc.
Generally, Wikipedia and Maps services has already done description of most publicly known [N], [O], [P].
People in their blogs and diaries mostly write about [E], [S]. People on messengers also mostly talk about [E], [S]. However, sometimes people want to describe non-publicly, the [N], [O], [P] that only they know of, and share it only with specific people (e.g., my kitten, my dog, my lover x, our trip y etc.), because it is generally these non-public items, that people's personal goals are associated with, and people need tools to talk about more efficiently and in a more organized way. E.g., people do want to talk about specific vacation with specific friends only, or about specific friends with whom they want to improve relationships with, or specific people that need special care, etc., however, be able to later choose fragments of discussions which to share with whom, e.g., to share fragments of discussion with a doctor, or an analytics service run by an organization, and be able to retain the ability to control the content access, as long as the content would not go out of the personal domain (e.g., myname.me).
Moreover, when sharing any fraction of their content, people may want to include the expected re-share and re-use scopes. E.g., "you can re-share this with your strategic friends interested in..", or "you can re-share this with organizations, x,y,z, etc."? (extension of licensing?)