Sanding the fridge can help to create a smoother base for the primer and could also ensure a longer-lasting finish. However, I decided to skip this step and will report back on how it lasts long-term. For now, the paint went on wonderfully though and looks perfect, so I think that the decision is really up to you. It also depends on the finish of your refrigerator - is it smooth or not. If you do decide to sand the fridge, first clean it, sand it, re-clean (to get rid of any new dust), and then paint it with the primer coat.