Following brushing and interdental cleaning it is recommended that you rinse for 30 seconds with a mouthwash. In addition to providing further mechanical cleaning, most mouthwashes are formulated to serve a primary function, including; anti-bacterial (gum disease), fresh breath, fluoride (tooth decay), whitening, etc..
Note – while most mouthwashes are intended for regular daily use, however in the case of the chlorhexidine based anti-bacterial mouthwashes these should only be used as recommended by your dental professional.