Do I need a “shared address” if my email account is already shared?
You most likely don’t need any shared address if you have configured a shared account. Shared addresses are meant for situations where emails sent to multiple addresses end up in the same email account (e.g. email@example.com), but you only want to give your coworkers access to specific emails based on the alias they are sent to (e.g. firstname.lastname@example.org, email@example.com). You could create two shared addresses in such a case, each with different auto-sharing settings.