Danger to Children & Pets
It is easier than you might think to leave a door open or otherwise accidentally allow access to poison that will harm or even kill a curious child or pet. There is an antidote for it (Vitamin K) and stomachs can be pumped but it is still a very unhappy time for all involved and must be done quickly to avoid serious consequences.
It is also a possibility that a pet could eat a poisoned rodent that doesn't make it out of your home before it dies. We know of puppies that have died this way.
So, why take the chance???
It is therefore substantially better to exclude or repel rodents before they get in instead of taking the chance of having poison on the premises at all.