Soda and beer bottlers, to name a few. To floc and disinfect potable water. Basically for the same reasons as above. Plus it is 3,000 times faster acting than the traditional sanitizer, chlorine. The EPA is trying to eliminate chlorine as it is linked to cancer.
Ozone is much faster and more powerful than chlorine.
Just one, it has a residual that ozone does not. Accordingly, ozone only oxidizes while it is being bubbled in water. Chlorine, being a chemical, stays in the water, which is good because it continues to disinfect while the water is in the pipes, but bad because you digest the chlorine. If this is occurring, you probably are using too much ozone. However, you can run the off gas through carbon to destroy the excess discharge.