There are two types of mouth rinses. These are cosmetic and therapeutic. Cosmetic mouth rinses, or mouthwash as they are sometimes referred as mainly serve the purpose of freshening breath. The act of gargling and swishing the rinse in the mouth will remove some bacteria and debris. A therapeutic mouth rinse will do all of this but it also contains fluoride and has been proven to reduce plaque buildup, fight cavities and help to prevent gum disease (gingivitis).
It is important to note that mouth rinses, even therapeutic rinses, are only somewhat effective. This should be part of the daily routine in conjunction with flossing and brushing. Regular rinsing with water and a fluoride toothpaste is just as effective as a therapeutic mouth rinse.