title: Usage of apply plugin: 'application' tag in build.gradle file
body: <p>I am starting to explore gradle and the question might be naive. 
  I have noted from the gradle docs about below plugin-</p>
  
  <pre><code>apply plugin: 'application'
  The Application plugin facilitates creating an executable JVM application. It makes it easy to start the application locally during development.
  Applying the Application plugin also implicitly applies the Java plugin.
  </code></pre>
  
  <p>I want to understand if the below plugin entry is mandatory as I have not seen it in many projects. Also if this is used to make the jar runnable/creating executable JVM application. Does that mean skipping does not make the application executable ?</p>