The PMS is a forum integrated feature, that allows coordinating tasks and handling bugs. You can give priorities and make a task specific to a working group or single worker, and the person will be updated on his task. This management can help you a lot to organise your working steps and increase the efficiency. ;)
we offer much more then forums ;) if you decide to start a mod in bigger sizes like a total conversion, you need a place to discuss stuff privately in your team, and to organize what you are doing (Project management system). Also, for your mod material, you need enough webspace. I have worked on total conversions for Galactic Civilizations II, so I have some experience in that ;) Because of our friendship to stardock & envolvement on their games, we offer their fans
thx, Pure