Storing data?

I was reading an article where the author says it is not a good practice to store data in the DOM. Indeed this is a bad practice and you should avoid it. After that he gives an example with using the DOM with the ALT attribute:

$('selector').attr('alt', 'data being stored');
// later the data can be retrieved using:
$('selector').attr('alt');

and after that the more clean:

$('selector').data('paramtername', 'data being stored');
// then later getting the data with
$('selector').data('paramtername');

OK, is more clean. But however it is bad practice to use such a “heavy” construction to store local data. It is obvious you can prefer to store it in a local variable. Thus you avoid the extra performance.