Something that is not always readily apparent about an online community (or tool for socializing) is that features do not define the utility of the tool. Because the net benefit of the tool is the socializing and sharing, the culture within the community tends to define how the tool is used and how users benefit.

Facebook has a culture of sharing entertainment of any kind with people you know.

Google+ has a culture of sharing experiences and photographs with people that share your interests.

Some of this culture evolved from how the tool was built, in particular how you lump people into circles relating to topics of interest and channels of physical connection, as well as how the content is displayed to the users.

Most users will decide on the community culture they want to be a part of.