This is just a placeholder to experiment with using topics to generate specific subject specific feeds within the same blog. If this post was related to psychology, for example, and everyone agreed to use the same psychology tags on all of their posts, than everyone working on the cooperative blogging project could use the same blog, and people would have the option to subscribing the the feed for the entire blog or for just posts tagged with the subject(s) of their choice.
This would give people posting the option of posting something to more than one category. The other option is to maintain separate blogs for each subject, but I like the combined blog better.