This is a fantastic sanitizer as lowering the pH of the dilute bleach solution with acetic acid shifts the equilibrium to favor hypochlorous acid (HOCl) instead of the hypochlorous anion (-OCl). Hypochlorous acid is far, far, far more effective in sanitation than hypochlorous anion.
Just don’t be stupid and add bleach directly to vinegar or you will get blown away by a puff of chlorine gas. At best you’ll be left with stinging eyes and a headache. At worst you could die if a large enough volume was mixed in a poorly ventilated area. In a very dilute solution as Mark describes, it is a perfectly safe sanitizing mixture. Just add the bleach to the water first, then add the vinegar.