"Periodic job" check box functionality in the start variant of a process ch

Double click any start variant of a process chain, then click Change Selections button, the Start Time window pops up with Some buttons on the top like "Immediate", "Date/Time", "After job", "After event", and etc., and at the bottom of the window, there is a check box called "Periodic job". We are not sure the functionality of this check box, is it only related to the "Date/Time" button when setting up a schedule run? Does it function if the process chain is triggered by an event and the event is triggered by a daily job? Also does it function if the button "Immediate" is clicked?

Thanks