Unless an educational institution has an extremely large venue to hold its graduation ceremonies in, it is common to see the institutions limit the number of attendees each graduate can invite to the ceremony.
When invitations to the ceremony are limited, graduation announcements may be sent to close family members and friends who could not be invited to the ceremony. Graduation announcements are intended to be a means to share the exciting news. They carry no obligation to send a gift.
Announcements are only sent at the time of graduation. If a student cannot walk with their class for academic reasons, they must wait until they receive their diploma before sending announcements.