These settings are similar to the RSS/Podcast settings, but for setting up to publish an iCal Events feed used by many calendar programs. To enable the iCal feed feature, it must be enabled. This will also present a link next to the calendar name.
You may also select how many days of events to 'publish', with 365 being the default. There is also a setting to tell the 'calendar program' how often it should expect events to be updated and request a new update. The default is 60 minutes.