Julie, in the grand scheme of things, our purpose is to build an accurate and well sourced tree here. Since we're all volunteers, a more specific description of "our purpose" can't be dictated by someone who pays us money in exchange for doing something his/her way. The result is that "our purpose" is probably defined in as many ways as the number of individuals included in "us", with all the individual versions meeting a description of contributing toward that overarching goal.
While we are all in agreement (I hope) that the goal is to have a well sourced tree, we all go about it differently. Some only work on their own family, others work on specific groups of people - maybe by historical association, maybe by culture, maybe by affiliation in a group or an historical event. It also continues down to how we work - some put a sourced timeline in the biography, others write prose, some put a lot of effort into eye candy (graphic decorations), and some take pride in cleaning up the mess left by others. I've done, and continue to do, my share of mess-cleaning, but don't hold it against anyone else who doesn't care to contribute to that … and now, the day has arrived that I'm one of the makers of the messes, which I will work on, but probably won't ever finish cleaning up.