In magento xmlconnect_notification_send_all is a core cron job.
What is exact purpose and scope of xmlconnect_notification_send_all cron job?
Mage_XmlConnect module is used for managing and configuring the mobile application connected to your website (if you have one).
I'm not 100% sure but I think that cron is used to send push notifications to the app users.
Off topic: If you don't have a mobile app you can disable that module by adding a new file in
app/etc/modules. Call it
Zzzz.xml (so it's loaded last) with the following content
<?xml version="1.0"?> <config> <modules> <Mage_XmlConnect> <active>false</active> </Mage_XmlConnect> </modules> </config>