It does add value as all javascript code should run in strict mode so that it prevents certain actions from being taken such as gaining access to the global object. Secondly, it is faster that jshint, eslint and jslint. Few characters do not add tons of bytes anyway. As this library is going to be minified anyway in release applications therefore, it size will be reduced thus will not affect app performance.
Added EcmaScript 5 'use strict' so that the code runs in strict mode.