The hidden field is by definition 'invisible', so there isn't a lot to see. However, it can be useful to keep an id :
Note that <hiddenFieldInstance>.getValue() returns the value as stored, without type casting (we store an integer -> we get an integer).
However, when the form is submitted via a 'submit' button, the hidden value is sent as 'string' whatever its datatype was... (we store 12, we submit "12").
This is a limitation of the classic HTML form submit. To circumvent the problem, use an ajax submit of the form (which relies on getValue) : see form examples.