I carried a health certificate for our dog since she had a chronic health condition and I felt if I needed a vet it would be helpful to them. We were a 4 hour time difference from out vet, so making a phone call to them may not have been possible. Fortunately I never needed it, but I would have rather had and not needed it than not had it and needed it. I was only asked for her rabies certificate once. I think most of the time she was never noticed sleeping on the back seat and we were not asked about her.