html5 - What does the value attribute mean for checkboxes in HTML?

I hope I understand your question right.

The value attribute defines a value which is sent by a POST request (i.e. You have an HTML form submitted to a server).
Now the server gets the name (if defined) and the value.

    Is it worth?

The server would receive mycheckbox with the value of 1.

in PHP, this POST variable is stored in an array as $_POST['mycheckbox'] which contains 1.