Let's say you want to manually activate traders or otherwise check customers first before moving them to another (better?) customer group.
But - don't you think that the customer will notice this by himself. Of course, you will constantly have emails saying "am I activated yet?" instead of the customer checking by himself. So you write an e-mail every time.
With this module, all you have to do is tick "Notify customer of change?" and an email goes out with a predefined text.
You simply tell us what you want it to say when you place the order.