The most customizable aspect of the user interface your application delivers is the one provided by Salesforce through its highly customizable layout editor that provides the ability to customize the standard user interface pages (including those now delivered via the mobile client Salesforce1) used to list, create, edit, and delete records.
In contrast, a user interface constructed with Visualforce applying customization features takes added effort on behalf of the developer typically utilizing Custom Settings and Fieldsets. Visualforce pages can be used to customize parts of or completely replace the standard user interface. This will be covered in more detail in Chapter 8, User Interface.