When you share a Calendar with a Grantee who has manager permissions, the Grantee can manage your calendar for you, including doing the following:
Create meeting invitations and send them out on your behalf
Accept and decline meeting invitations on the your behalf.
Change meeting details
Delete activities from the your calendar
When the Grantee sends an email message in response to a meeting on your calendar, the return message header shows the From as the admin's address and an On Behalf Of address as your address.