One common theme in the development world is the vast difference in productivity between individual practitioners. Among folks with similar backgrounds, some are easily 10x more productive at delivering functional software. Software development is obviously not alone in having to deal with this, but I there are some particular attributes of software development that make dealing with this mismatch particularly difficult.
The first problem is that many people seem to have the mistaken impression that if one has developers who produce output, then the output is simply the sum of the individual outputs. This is just not true by any reasonable measure and is a contributing factor to the reason many outsourcing projects end up a smoldering mess. Mathematically, each developer adds a cumulative amount of drag if the software they are writing needs to communicate with software other folks on the team are writing.
As an example, suppose we have 1 developer working on a project, and he has a perfect understanding of the requirements. The overhead for this person to write the software is the cost of typing it into a computer, compiling (if necessary), and deploying it. Obviously the frequency and cost of compiling and deploying are a factor, but this is typically a fixed cost.
Now let's add another developer who is going to work on the same software as the first. We now incur the overhead of the first developer communicating what he is doing to the second (and visa versa) PLUS the overhead of bringing the new developer up to speed on who things work. While bringing the new developer up to speed is a one time cost, the communication overhead is ongoing. Generally speaking, the communication overhead can be represented as a complete graph with a formula of cost=(count*(count-1)) /2.
What does this mean? Well, for starters, compared to a team of two, the communication overhead for a team of 10 is 45x higher and a team of 50 is 1225x higher! More importantly, this is assuming unrealistic perfect communication, so the real factor can be much larger depending on the effectiveness of communication. As an example, using high latency communication or off cycle team mates can often double the cost of each network interconnect.
But wait! we know there are software projects with tens, and even hundreds of developers, how can they possibly be successful?
For starters, many teams simply absorb this cost and they largely end up much less successful than they COULD be. Any project manager or even developer is probably familiar with the sad problem of having an initial spike of productivity with a small team, then looking on in dismay when an influx of new people to the project drops their delivery velocity.
A better approach approach is to reduce the amount of communication necessary between subgroups within the team. This can be done by choosing a software architecture that has well defined boundaries and focusing the communication between the independent teams on those boundaries. For example, many places do this by having a "backend team" that writes database access code and a "frontend team" that writes the GUI.
So in our example of our team of 10, if we broke it into two teams of 5 who intercommunicated via one interface, our communication overhead would be reduced to 21 from 45.... that cut it down by more than half!
What does this mean? It means by following these guidelines, project managers and architects now have another tool to account (literally) for a variety of team configurations. Information technology architecture is not JUST about software and hardware, but also wetware (people) and human factors need to be accounted for as part of the art.