Diseases that we vaccinate against include canine parvovirus gastro-enteritis which can be rapidly and unpleasantly fatal, and cat flu which can be recurrently debilitating throughout a cat's life, so it is very important that our pets are protected.
Equally, diseases like distemper are now so rare that many vets in practice have never seen them.
So how often should we vaccinate and against what? The manufacturer's Data Sheets give a recommended booster interval, and depending on the brand, this can vary from 12 months to 4 years. Oh, and to make it worse, the same vaccine can have different recommendations in different countries, so that's not much help.
The homeopaths (and no, they're not all mad) would say vaccinate as little as possible. I might also ask you when you were last vaccinated...
So what to do? You either follow the book and do as you're told, or you ask us about vaccine titre tests so that we only give booster vaccines when the antibody levels tell us that as vaccine is really needed.