Adding more people to a team because the team has more responsibilities than one person can handle is one thing. Needing "coding buddies" because you're lonely (which is what Jeff made it sound like) is another.
I can of course work on a team when the project is beyond the scope of a single developer. I prefer to work alone, since that entails exactly zero coordination overhead.
I think it may come down to the complexity of a project. For something non-trivial simply having someone to bounce ideas off of can make a big difference in one's overall efficiency, and thus probably happiness.
I agree, but I will also say that you can almost always find ways to get more done with more people. For example, it's easy to break up a project into code, css, html, javascript. That's four people right there. You could also have a graphics person drawing icons or cool backgrounds. You could have a database person. At some point you'll need a networking guru, marketer...
It's easy to get into the trap of thinking it's all about code, but there are lots of ways to add people. Sometimes, coders don't want to add people, because it's one more person asking them to code something. Coders often don't know how to push back and say, "This is what I'm working on, this is what I need you to do."
Every answer to an IT problem is "It Depends." In this case, the question of "Does adding more people make the project go faster or better?" is "It depends."
This question can't be answered with a general absolute.
"For example, it's easy to break up a project into code, css, html, javascript."
That sounds awful. That's three people who have to coordinate in order to display a new data element, and a fourth if the new data element has any kind of interactive functionality.
It's much better to break the project up into functionally independent pieces, and have developers who can work with all of the technologies each piece touches. You're much more likely to lower coordination overhead that way.
I can of course work on a team when the project is beyond the scope of a single developer. I prefer to work alone, since that entails exactly zero coordination overhead.