A water flosser can help you get those spots that regular flossing cannot reach. It can get bacteria and food, before it turns into plaque. It can help with gingivitis and periodontal disease, which is irreversible, since gums do not grow back. It can prevent gum disease and bleeding of the gums.

It can get hard to reach places due to bridges, caps, and so on. It can help prevent cavities. It shouldn't replace regular flossing though.

I started using a water flosser, when I found out I had periodontal disease, sever gum disease, since I had my daughters. I wanted to do everything to prevent my gum disease from getting worse.