Because they might not stay in the Barbarian Cave for the next while, Sanders decided to take Angel to report their upcoming itinerary first.
Normally, leaving didn't actually require a special report. Many wizards often decided on the spur of the moment not to return for a while, like Madeline, who had initially left the Barbarian Cave for a short time, only to later decide to stay in the Abyss to study Black Thorn. These sudden changes of plans were too numerous, and generally, if one were gone for over a decade, such short-term leaves did not need to be officially reported.
Generally speaking, reporting one's itinerary was only required for Apprentices and Official Wizards who were certain they wouldn't return for a long time. Take Zithraide, for example, when he left the Barbarian Cave, he had no intention to return anytime soon, and it has been nearly two hundred years since he left.
