It's "easy" solely in terms of the programmer modifying the code. Always putting a comma at the end of the array prevents errors like the following:

# before
@array = (
          'dog',
          'cat',
          'fish'
         );

# after
@array = (
          'dog',
          'cat',
          'fish'
          'bird',
          'rabbit'
         );
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Including the trailing comma means when you add new items to the array, you don't have to do anything besides adding the new items.