When to Use Salesforce User Interface API

• Build Salesforce UI for native mobile apps and custom web apps using the same API that Salesforce uses to build Lightning Experience and Salesforce for Android, iOS, and mobile web. 
• Build user interfaces that let users work with records, list views, actions, favorites, and more. 
• Not only do you get data and metadata in a single response, but the response matches metadata changes made to the org by Salesforce admins. 
• You don’t have to worry about layouts, picklists, field-level security, or sharing—all you have to do is build an app that users love.

Read More: When To Use Salesforce REST API  
                   When To Use Salesforce SOAP API 
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                   When To Use Salesforce Chatter API