Tl;dr: Apparently Apple Geniuses ask customers who are dropping off their Mac for an off-site repair to turn off their admin password.
Despite the fact that: access is not needed for some repairs where they ask that Question and there's a more secure option available: transferring the device password to Apple's CRM, where its use is auditable.
Despite the fact that: access is not needed for some repairs where they ask that Question and there's a more secure option available: transferring the device password to Apple's CRM, where its use is auditable.