whats is the use of hidden and none ?

Question

if we dont want to show that element then why we will insert in it?

Answer 1

For example: when inserting a correct e-mail in a form with JavaScript DOM, the div "error" is default hidden, but if there's a wrong e-mail, JavaScript DOM will change the element's visibility ans show the error.

Answer 2

This function is very useful when tou use JavaScript DOM.
JavaScript will do the functions, such as show that div and show something :)