Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Yes, you understand correctly when you are talking about an Office 2016 license (not an Office 365 license). Of course you also need the product key.
But giving someone else, even "tech support", your email account and PASSWORD violates one of the basic rules of personal and corporate security "best practices". Sure the user should be then required to immediately change their password, but ... you know users ...
And you also have to keep track of the product key, the email account and the computer ID somewhere for a time when the license has to be re-installed or transferred to a new computer. You CANNOT depend on the user to keep track of that info. And you can no longer use the product key "extraction" tools since MS "improved" that option out of existence.
Sure it is manageable if you are talking about a single install. But if you are providing support for a large company, installing many new computers or many new Office 2016 licenses it does become complex and time consuming for the computer support staff. Someone has to "eat the cost" on this extra time required for installing Office.