No this is in addition to the forums, galleries, etc. Its just an easy way to have everything all together but the other things will stay as they are. We had sub communities back on the old .ez platform as well. 

Some people, especially newer members get lost trying to find everything and this is an easy way to keep up with your favorite area(s) of interest.

You don't have to use them at all, its just for those that want to easily see whats going on in a specific area...