I’ve written this same basic argument for small teams three or four times now, so to comply with the Don’t Repeat Yourself (DRY) principle I though I’d post it. In short, this argument repeats Brooks’ Mythical Man-Month concept 🙂 , and asserts that you must restructure the communications dynamics of a team when it changes in size, regardless of whether or not your project is late.
To paraphrase one of the points made in Frederick Brooks’ The Mythical Man Month, complexity in a system scales with the number of interfaces. Applied to a team communications system of N people, the worst-case number of total communications channels is when everybody talks to everybody else. This can be expressed by N(N-1)/2. In other words, a given person in the team (the Nth person) is communicating with everyone else (N-1 people). So the problem with large horizontal teams is that as N increases, the communications overhead of being able to operate has the potential to increase exponentially.
As a member of a 5 person team, keeping open, frequent communication with 4 others is no big deal. Even with 5(5-1)/2 = 10 different relationship combinations, all 5 people can keep current with the other 4.
If this team grows to 15 people, however, communicating is not as simple. In the worst case, not only do you have to communicate with 14 other peers, there are now 15(15-1)/2 = 105 total relationships between people, each with their own dynamics and influences. The team is only 3x bigger, but now has 10.5x the number of interpersonal relationships. And the majority of the information going across those channels may be irrelevant to your job, but if it’s relevant to the team as a whole, you’ll be sucked into meetings and email threads spending time and mental cycles just on overhead of keeping the collective ship floating in the right direction.
Now, this is all worst-case abstract theory, but does highlight the scaling problems of communication in teams of fluctuating size. As your team scales, you need to reevaluate communication culture to keep operating overhead low and excessive communication to a minimum.