Suitelets use UI objects to create custom pages that look like NetSuite pages. SuiteScript UI objects encapsulate the elements for building NetSuite-looking portlets, forms, fields, sublists, tabs, lists, and columns.
Backend Suitelets do not use any UI objects and execute backend logic, which can then be parsed by other parts of a custom application. Backend Suitelets are best used for the following purposes:
Providing a service for backend logic to other SuiteScripts.
Offloading server logic from client scripts to a backend Suitelet shipped without source code to protect sensitive intellectual property.