title: SparkContext.getOrCreate() purpose
body: <p>What is the purpose of the <code>getOrCreate</code> method from <code>SparkContext</code> class? I don't understand when we should use this method.</p>
  
  <p>If I have 2 spark applications that are run with <code>spark-submit</code>, and in the main method I instantiate the spark context with <code>SparkContext.getOrCreate</code>, both app will have the same context? </p>
  
  <p>Or the purpose is simpler, and the only purpose is when I create a spark app, and I don't want to send the spark context as a parameter to a method, and I will get it as a singleton object?</p>