Salesforce puts a lot of effort into its desktop and mobile based UIs. These declarative UIs are the first to see advancements, such as the ability to embed reporting charts. These standard user interfaces are also the primary method by which your subscribers will customize your application's appearance. Furthermore, the UI will evolve with Salesforce's frequent updates. In some cases, new features are available to your users, even without you updating your application.
Tip
In general, aspects of your application that had already leveraged the standard UI in Salesforce Classic will just work fine in Lightning Experience without change, and will also automatically adopt the new look and feel. However, if you have utilized Visualforce extensively, and/or used unsupported features such as JavaScript Custom Buttons, you will have to make some changes. Carefully test and explore your application in Lightning Experience to understand what changes you need to...
