For example, at the end of a Wheel and Deal from a two-faced line, the two couples have just finished "wheeling" into position to face each other. For a Wheel and Deal and Sweep 1/4 they just keep circling in the same direction, while still facing each other.
Another common case is Flutterwheel. The dancers already have a circling motion as the dancers who started on the right come back to their own side of the box. For Flutterwheel and Sweep 1/4 they just continue that circling motion for another 1/4.
Note that the action of Sweep 1/4 is similar to the four dancers doing either a Circle Left 1/4 or a Circle Right 1/4, except that they don't actually join hands to make a circle. They just stay as facing couples the whole time.