"Do I really need to prime first?"
If you've asked this question, you are definitely not alone. I wanted to share a couple resources that can help you determine when and why you should prime and what Zinsser products would be best. The type of substrate, condition of surface, whether the item will be used indoors or out all make a difference.
1) This quick-read article summarizes the greatest benefits of priming so if you're not sure if you should prime, hopefully this will help you determine the advantage that priming will have on your project.
2) Once you've decided if you need to prime, the attached handy Zinsser primer chart features solutions for all your interior and exterior projects. Just find the substrate you are painting and see which primer would be the best for your project. It also highlights primers that cover stains like tannin bleed, mildew, rust as well as seal in odors from nicotine, pets and more.