Use of "uses" in router of Laravel

I have written this and it is working.

Route::get( 'users', [ 'uses' => 'UsersController@index'] );

Now i am removing the "uses" and it is still working.

Route::get( 'users', 'UsersController@index' );

What is the requirement of "uses" here. Pleas give the view with reference url.

via Chebli Mohamed