There are small advantages, in that if a mod has several components, all would be coded the same way, and the look and feel of all mods should stay consistent. However, over time I've changed my opinion on this a bit.

The major disadvantage comes into play if someone is busy, loses interest for a time, or just has too much to do. Cide hasn't wanted to code much since last year, which really makes it impossible to make any changes or updates. I can't code myself, so I end up relying on him to want to fix a bug or make a change. When a project has multiple coders working on it, if one isn't going to fix a bug, another can, and I see that as a huge advantage with keeping things up to date. It has crippled our projects over the past several months.