The lone developer in a team was called "the guy in a room" in a book called The Dynamics of Software Development. Good advice against this dynamic for the good of the team and the developer can be found on the Coding Horror blog.
Sometimes "alone on a team" is related to the needs of an assignment (one developer is enough, more would be overkill). Sometimes it is a consequence of attempts to separate a developer from other developers due to personal differences. Sometimes this kind of exile is self imposed. The developer doesn't want to work with others for any number of reasons like: he doesn't know how, others don't want to work with him due to eccentricities, skill/quality/speed of the work may lead to isolation, or he is simply belligerence. The opposite case where although technically sound, the developer fails to be assertive, so working alone is a route to having a sense of control over project decisions. Whatever the reason, I believe it is less effective in the long run to have insular developers. Solutions range from partitioning project differently, conflict management, training, team building, to disciplinary action.
Diversity is a benefit for teams. However, sometimes things can go wrong and people who can benefit from working together are excluded because people with things in common form a clique, excluding the other people. Teams can divide artificially based on age, politics, religion, national origin, race, sex, what degree they hold, where they went to school, what sports they like to watch or play, and a host of other silly reasons.
A few years ago, I traveled with a team of developers from our office to another office for training. The two offices were in different states, but within the same region, so culturally, there should have been little difference. There were important incentives for our team to engage with the other team. Our customer had a failing business and our project was cancelled. In contrast, they had a thriving business and we were being assigned parts of it.
However, the entire time we were there, the team from my office ate together, drank together, and sought out entertainment together, with little or no interaction. Perhaps it was a throw back to high school sports culture where we were the away team and they were the home team, and out of habit, competition was the paradigm and cooperation was atypical. Even in their lunchroom, where in theory food induces a certain level of casual mingling, four days of joint training passed with both teams in the same room, but barely interacting.
You don't want to know the result of this awkward partnership, but I can tell you it lasted less than two years. Management tried many things to integrate the teams. A vice president from our facility took over important functions at a high level, my supervisor became a manager for the other team, and I worked for a supervisor at the other facility who had been working to earn the manager position for about 15 years including many years as a start up.
Even with extensive restructuring to create cross site communication and engagement, I was one of only a few people who had daily interaction with multiple members of the remote team. Occasionally, I had conversations with managers from the remote site and was shocked that even after a year or more, they had so little interaction with members of their remote team that they could not recall the name of one of their direct reports. Not sure if it was the fault of the manager or the subordinate, but it certainly showed a serious problem with "alone on a team" that was compounded by geographical distance.
