I suppose that because because of the updated way that the Calendar application is integrated into the OS X system and the notification area the "calendar agent" needs to constantly run in the background on OS X ML.
I see it making a lot of requests when I debug the HTTP(s) requests on the system:
The requests stop if I do
How can I keep the calendar agent from running in the background?
ps: I also tried removing the calendar from the notification area without luck: