If set to false, the email1, email_addresses_non_primary, invalid_email, email_opt_out, and email_and_name1 fields are used. Otherwise, a single email field, storing a JSON array with emails and all their settings is used.
Note that SugarCRM Developers consider the old approach with using email1 and other email-related fields out-of-date, deprecated, and subject to removal in upcoming Sugar releases. We keep the ability to use it for compatibility purposes, but recommend using the new approach. Read more about this in SugarCRM developer blog.