During site import/duplicate email notifications are sent.
Note: The default behavior is to set the announcements as drafts in which case no notifications are ever sent but if you are using the option
When announcements are not set as draft on import then email notifications are delivered, which is also not ideal. If creating many sites this can quickly generate a lot of email. Also note that if notifications are not sent when they are imported then there is never any notification sent.
Given this info it is more undesirable to send email during an import.