Pet hair sticks to the fibers of the fabric and can be very difficult to remove. If you have a pet that sheds its coat and you carry them in the vehicle to go for walks or to the vets then there is a high chance that you will need the hairs removed at some point. 

If you have pet hairs in your vehicle you could be at risk to having the smell of your pet lingering and removing them will aid in keeping your vehicle smelling clean and fresh.