Well, as the world's worst worrier anyway, I think I'd feel happier if I can see that they have a high titre, and the only way I'd know that is to get the test done.
If the titre comes back lower than the lab uses for its "scale" I will probably just get my vet to vaccinate against the disease showing the low reading, (as long as my vet can obtain the single vaccine.)
So,I could still be vaccinating when there was no need, I suppose, but I'd still feel that I was minimising any risk I was concerned about by giving yearly all-in-one boosters.
(One of my dogs came from a breeder who, despite having generations of cavaliers, rarely had a dog needing veterinary treatment. This breeder is also a registered homoeopath, and it may be a coincidence, but in 25 years of owning cavaliers, we have never had such a healthy little dog as the one she bred!) And the only thing we have done differently with the two cavaliers we have, is not going along the yearly booster route. Could be pure coincidence, of course!
Sami

Well done for finding Chris Day, Sami!  He was the Vet who was debating with the Intervet Vet, and that debate was the final straw that made me make my decision not to vaccinate any more.

I started my nosode regime under his guidance.

He has Cavaliers with no immune systems after vaccinations/boosters coming out of his ears!!  I sent him 4 in the year before I retired from grooming! :(