Newsletter lists should be as recent/fresh as possible. We have a lot of dailies and it’s critical opt-ins start receiving their first issue with the next issue available. If they sign up for a daily, they should get a newsletter the next day or they tend to forget.
They can create the campaign in advance without sending it, then refresh the HTML as they make changes before the final deployment date.
For unsubs, when a list is applied to a newsletter, the filter is always "up to the minute" with unsubs. They will be filtered out at the time of deployment.
Also, when ads and content are being scheduled into newsletters, they can be previewed without creating a new campaign. The campaign creation step can be reserved until the day of send, or just before, which will prevent the list from being pulled too soon.