The book “The Mythical Man-Month“* discusses some of the reasons that larger teams are inefficient. The main concern is with the number of possible connections between team members. If you have two team members, there’s only one channel of communication. However, if you have n team members, then you have n(n-1)/2 channels… which grows quickly (order n^2) as n becomes larger. If one is required to work with a large team, say more than 10 to 12 people, it becomes imperative to find ways to improve communication efficiency.
One of the best ways to do this is to use broadcast mode communications. Information radiators are a simple broadcast mode tool. In a subtler way, having the team co-located** also takes advantage of broadcast mode communication: if everyone can overhear all the conversations that are going on in a room, then people can tune in when they hear something of relevance.
It is important to note that there are several other forms of broadcast communication that are useful in certain circumstances: e-mail, blogs with RSS or Atom feeds, analog radio, television (if you can think of others, please let me know in the comments). These tend to be more useful for very large communities. Radio and television have severe limits: they are not easily used in a communal fashion.
Some forms of communication may seem to be broadcast, but in fact are not. A simple web site is not because it requires that people poll it to see if it has been updated. Conference calls are marginally broadcast in that while they are occuring, everyone participating hears everyone else. However, a conference call requires active synchronized attention on the part of all the participants.
**A search on dictionary.com for collocation indicates that three spellings are all correct: collocate, colocate, and co-locate, this latter spelling being the most common on the web.