Yes, the "system" module is just a term we use but it could also be Structure. It is not inherit to they system at all, but helps with mapping, filtering, master/meta data of lists. The one above is based off of Time, where you can do the mapping to the Month Names as well as filter out all quarters or years. Another example could be on the base member of a Product Hierarchy where you are figuring out what the parents are (P3, P2, P1). If you have these in one module, all module builders will know where to get the data instead of recreating the wheel in their own modules.
Again, the main benefits are:
Hope this helps,