Just to add my two cents worth.
We recently flew our venerable UH-1N (ex Canadian Air Force) with an offset lateral CG, for a stability and control exercise. With the ball centered, in cruise, we had about 10-12 degrees of sideslip, and when we flew with the ball in the same position it was in when hovering into wind, (about half a ball to the left), we had nearly zero sideslip.
Keeping the ball where it is in the hover gets my vote every time for ease of flying.
The string also works well in a high power climb with any airspeed above about 30 KIAS, and gives much better performance than using the ball.
For flight testing for performance, we use the slip string anytime we're below 60 KIAS, just for consistency.
Does anyone have an STC for a slip string on the Bell machines?