Is mouthwash beneficial? what does it do that brushing can't?

Yes : Combined with brushing and flossing, it will aid in the fight against gingivitis. Listerine with its essential oils has been proven to reduce gingivitis. Some rinses with Fluoride like act help with caries reduction. Salt water can be healing. However nothing is better than brushing and flossing.

Yes: Studies have shown that mouthrinses can decrease the number of bacteria that are involved in tooth decay and or gum disease. Toothbrushing on the otherhand with floss is the most effective method to mechanically and effectively remove dental plaque the primary cause of tooth decay and gum infections.