It hinders because the rat can always be tracked down by simply following the stale Garlic smell, which is why the rat tries to live in windy places where its odour is carried away on the breeze. The benefits are that even if an animal tries to bite the rat, the rat will just breathe over its attacker, who will run away quickly to get some fresh air without pursuing the attack.
Even hawks and owls are put off. If a rat senses it’s about to be attacked by a raptor, it rolls onto its back and breathes and breaks wind simultaneously, filling the air with a pungent aroma that causes the bird to fly off coughing fitfully. Thankfully for the rat, its own sense of smell is poor, allowing the rodent to breed profusely.
This is an extract from the book Animals Evolution Avoided