Following on from the useful advice already offered, I came across an article from Helicopters Magazine's Fall 2007 issue that had a flight test of the MD902 Explorer.
The pilot/author wrote the following:
"Still, one must be careful to keep the ball centered as any deflection causes an increase in fan pitch thereby using engine power. For instance, at gross weight, a slip with the ball touching the right vertical line will reduce the rate of climb by 200 fpm while slipping in cruise can increase torque significantly. Flying without yaw in level cruising flight is quite important as slight displacement of a pedal will cause the helicopter to sashay somewhat."
Ken Armstrong, Helicopters Magazine,
http://www.helicoptersmagazine.com/content/view/465/132/
Further proof, should it be needed (!), of the importance of maintaining balanced flight. However, as the Explorers I am familiar with don't have slip strings, it doesn't add much to the string vs. ball discussion!
Simon
PS I hope the author of the article doesn't object to the direct quotation - I couldn't find contact details to seek permission.