Once a schedule is published any modifications to the schedule will automatically be added to staff calendars. The Send Changes to Staff button sends out the corresponding messages.
The reason changes to a published schedule update staff calendars immediately is because RecStaff has real time staff availability.
If you share staff with another department and were to make changes to a staff members shift the other department needs to know immediately what that staff members availability is so they don't schedule them for the same time and create a scheduling conflict.