Distribution of activities ensures that everyone does part of the job that best fits him. One can do posting, one can do only blog template design and one can work only on blog promotion. If blog niche is wider, every blogger can have special category inside that niche.
Advantages of complementary blogging are obvious. This type of group blogging is clear example where such blogging wins over solo projects. Single blogger will never be able to do amount of work that team of bloggers can do.
Let's take blogging about politics as example, especially, about politics in USA. During election year complementary bloggers can write from both democrats (one blogger) and republicans (another blogger) point of view. Another example would be blogging about relationships where two complementary bloggers can write from different sex point of view. Possibilities are endless. Even better if there are more than two authors. There is blog about programming where every blogger writes about one programming language: PHP, C++, Perl, Java, etc. This blog is updated more than once a day, has many visitors, RSS subscribers and excellent income from advertisements.
Blogs produced from complementary blogging have richer and more objective content. This contributes to blog quality, which then leads to blog success.
