What advantage is there in having the special sensory organs confined to the head region?

The answer to this question would be: rapid impulse transmission.

By having organ near the head, the brain can process the information faster because the length of the nerve that carries the impulse from organ would be much shorter. The nerve also at lower risk of damage since it was shorter.

But it makes the head very important and damage to the head can cause much more problem than any part of the body.