In the follower model, the user is always interacting with the majority or all of her following. When you post something on a network developed around a follower model, your potential reach is the number of followers you have.
This model’s focus on reach comes at the expense of privacy and deep relationship links. Unless you’re taking the extra step to protect your messages (meaning that people who wish to follow you must get your permission), you don’t get to choose who is part of your social circle or to whom you broadcast messages. People will follow you based on shared interests, the appeal or relevance of your messages, or any number of other reasons.
Social relationships formed within this type of model tend to be limited and shallow. The focus here is more on the “what” (messages and updates that are posted) and less on the “who” (the person posting them). Implementers of this model tend to limit the amount of information that can be posted in a single message or update, and may provide only a very limited amount of social information about the individual. This means that you will not get the same depth of social relationships that you might from a more relationship-centric model.
As you might have guessed, Twitter is a prime example of the follower model. Through Twitter, users post messages (“tweets”) that reach their followers. Followers may in turn retweet those posts (in most cases, giving the original user proper attribution) to their followers, ...