Once Community Hub is set up, you can customize it in a myriad of different ways; from automating user creation, to defining your password policies, and more.
Constituents are, in their own way, the backbone of any association. Providing them with the tools to succeed and flourish, and knowing how to help when issues arise are key components of a successful Community Hub.
Imagine going to a restaurant and looking forward to an amazing meal, only to find out that no matter what you get for your meal, the only side available to you is french fries. Some people would be thrilled, who doesn't like fries after all, but most of us would be a bit disappointed by the lack of choice available to us. That is what the Additional Settings gives you - if you just want the regular, you don't necessarily need these, but if you're looking for additional options? Well, you have them in spades.