In cha-cha, it’s two, three, four-AND-one. In “on 1” salsa, the “and” happens on the silent counts 4 and 8 (in “on 2” salsa, it’s on counts 5 and 1). In hustle, the direction (side, back or forward) of the “and” prior to one directs where the follower moves on count one.
In the sugar push step of west coast swing, the “and” count between 3 and 4 is when the follower’s momentum is absorbed and redirected from forward to backward. More importantly in this dance (and similarly in lindy and some other swing dances), the “and-a” before count 1 is where the stretch, the breath and much of the overall energy of the dance occurs.