You can customize site definitions and add functionality to list editing tools, but if your branding and tools strategies aren’t implemented in your list definitions, then your site isn’t completely following those strategies. Find out how list definitions work, what their relationship is to site definitions, and how to change the appearance and the structure of the list.
When you’re trying to change the way that SharePoint appears and operates to something more in-line with what your organization needs, you’ll find that modifying the site definition to change the appearance is a good first start. As you get more advanced, you may decide that you need to add functionality to the SharePoint list editing tools, or make other changes that impact how the user edits data in SharePoint. Ultimately, however, pushing branding or your additional tools down and into the site whenever a list is created means changing the list definition.
While you can create site templates with changes bundled in to implement your specific branding and tools, when a new list is created, it is created using the rules stored in the list definition. If your branding and tools changes aren’t in that list definition, then the new list that the user creates won’t follow your branding or tools strategy.
List definitions also allow you to define new fields in a list—but not just new fields to store data, which can be done from the user interface, but also the ability to define new types of fields that behave in new ways. For instance, it is possible to create a variant of the links list that allows you to specify whether you want the links to open up in a new window or not. This additional flexibility can be essential to implementing enhanced list types.