Vaccinations...good or bad?

I understand that there is a lot of controversy about vaccinating your pets every year. Don't misunderstand, animals must be vaccinated, but every year??? Humans don't get vaccinated every year, why do our pets? And heartworm...are the expensive tests really necessary?
I admit, I have not done any research into these alligations. But the rumors I have heard concern me (financially and for the health of my pets). Has anyone heard any information on the subject?
Sunnysky7222