Our parents and teachers would like to have the ability to click on an event--particularly when they are viewing it on their mobile devices--and add it to their personal calendar. Some people don't want the entire calendar on their personal calendar by using iCal, but they would like an option to easily click and add single events. 

When you have a doctor's, massage or fitness class appointment, you typically get an email with an attachment ending in "ics" to add the event to your mobile calendar. I'm not sure if this would be the same concept.