$c->default_privileges = array('read-free-busy', 'schedule-deliver');
default: array('read-free-busy', 'schedule-deliver')
These are the default privileges granted by new users to all other users on the system. The default values of 'read-free-busy' and 'schedule-deliver' mean that any system user will be able to see the new user's free/busy time, and will be able to invite them to meetings and respond to invitations from them.
Everyone can see everything
In a small office environment you may want to simply allow everyone to see everyone else's calendar, and so you can add the 'read' and 'read-current-user-privilege-set' privileges into the list.
$c->default_privileges = array('read', 'read-current-user-privilege-set', 'read-free-busy', 'schedule-deliver');
In a setup where many unrelated groups have access to the calendar server, you may wish to deny invitations by default, as they could be used for spamming other users. You should switch the 'schedule-deliver' privilege to 'schedule-query-freebusy'.
$c->default_privileges = array('read-free-busy', 'schedule-query-free-busy');
Possibly you might also add 'schedule-deliver-reply' in it's place so that if some users do choose to allow people to send invitations to them, it is possible for replies to those invitations to be delivered.
$c->default_privileges = array('read-free-busy', 'schedule-query-free-busy', 'schedule-deliver-reply');
Available from DAViCal version: 0.9.8.1 and later