Geeklog's calendaring system now allows users to manage their own personal calendar similar to Yahoo mail. If you check that checkbox then you are saying you want to allow users the ability to use that feature. If you don't select it then only the Site calendar will be enabled. The site calendar holds events for the general public to view and, generally, pertain to the content of the site it is on.
The reason people blame things on previous generations is that there's only one other choice.