A database template is a Domino database that is named as the Template database for a specific application. The most commonly customized Domino template in a Domino environment is the Mail template.
By customizing the design of the Mail template, all the mailboxes on your Domino Mail server can be enhanced, customized, or updated at once. Templates make it easier to manage the design of multiple instances of a common application (like Mail) by making changes to only a single template database (see Figure 1).
Figure 1 Making changes to a template lets you proof your changes and makes it easy to distribute changes to all copies of an application.
Domino development can be done "live," directly against an application's structure (not recommended for any production environment), but most likely would be done by creating templates and using them to distribute the changes to production.
You make your changes to a template application in your development environment. Once your changes have been tested and verified, you can use the Notes Client or your Domino Server to update the design of your production templates, distributing the modifications to any application that inherits from the template.
The "Designer" process on your Domino server usually runs at 1:00 a.m. and updates all Domino databases with all the changes that were made to the design templates that they inherit from.
Any new design elements in the template are added to the database that inherits from the template. Any elements removed from the template are removed from the database that inherits from it. Any modified elements in the database template are updated in the database that inherits from it.
This feature was designed with distributed applications in mind, making it easy to centrally manage the design of an application and to automatically distribute the application design to remote users or other parts of a larger Domino infrastructure.
Combined with replication, design updates are propagated to all the copies of a given application once they are replicated. Database templates make it very easy to distribute updates to your existing applications.