The Co-brand Default database allows a partner to automatically set up things like customizations, emails, campaigns and more for clients and have those copied over into all new client accounts.
Here is the full list of what can be duplicated:
Products and Product Categories
Tags and Tag Rules
To build out this database select that Account from your single sign on drop-don and choose your 'Co-Brand Default' database. Reminder: Everything in this account will be duplicated into the new account every time you sign a new customer.
Make sure you ONLY update things in this default database that you want updated for ALL NEW clients. All you have to do is create the items you want to be shared with your clients in the Default Database and they will be uploaded to a client's account once they sign up.
Note: any new additions to the Default Database will NOT be duplicated to existing client accounts. It will only be added when a new client signs up.