Most mouthwash should only be used occasionally and that means maybe once a week at the most. A lot contain alcohol, which helps destroy normal mouth flora and fauna. but even if they have no alcohol they contain anti-bacterial compounds which do similar things. Because the balance is upset then people start noticing bad breath and other issues and think the fix is to wash their mouth out again thereby compounding the problem. There is also some evidence that the alcohol also helps bad bacteria and compounds move from the oral cavity into the mouth tissues.
One of the best mouthwashes to use when needed is salt in a bit of water. It doesn’t disturb the normal bacteria and fauna too much yet the damaging bacteria don’t take to it very well at all. Good brushing and flossing take care of most of the plaque and associated bugs and then a rinse with salty water is a good finish if really required.
Fluoride is used to replace the lost minerals from your enamel that have been leached out by acids in your food but nature gave you the best refiller and that is your own saliva. Saliva contains a balance of minerals to replace the leached out ones but these days we drink a lot more acidic drinks (for example soft drink and fruit juices) and eat starchy and sugary foods that create an acid environment and feed the bad bacteria. So to assist your tooth health having some fluoride in your toothpaste is recommended to augment the job saliva does. Chewing sugar free gum after a drink and/or a meal can help as it tends to stimulate saliva production and thus helps your own body repair the damage and keep your breath fresher.
For those who suffer dry mouths because of medications or other problems there are some special gums and mouth rinses eg Biotene that have similar compounds to saliva in them to help keep your mouth healthier and therefore you happier
Some reading that might help:
and as a final bit on it from the LifeHacker website in response to a similar question "We presented your query to Dr. Mark Burhenne, a dentist and author with over 30 years of experience. Here’s what he had to say:
Over reliance on mouthwash is one of the biggest mistakes people make when caring for their teeth. Using antibacterial mouthwash can disrupt the normal flora (or bacteria count) in the mouth. What a lot of people don’t realize is that we rely on a healthy balance of good bacteria in the mouth to keep us healthy. Wiping all the bacteria out — good and bad — disrupts that delicate ecosystem of living bugs in the mouth and makes us prone to issues such as bad breath, oral yeast infections and cavities. I recommend to most of my patients that they ditch the mouthwash: you don’t need it. To prevent gingivitis, focus on oral hygiene, diet and an oral probiotic supplement. The mouthwash is a dangerous short-term solution that really has no efficacy at all."