That's a question that may be a bit vague, and also maybe a bit of a builing the house from the roof down situation? 😅
A harder rear ARB will give you less Rolling on the Rear End, and is something that helps against oversteer, typically mid-corner at slow to medium speeds. Alternatively a softer rear ARB helps against oversteering if the car is NOT rolling a lot on the rear.
It is NOT as simple as that though, since there are a lot of factors coming into play, and there are things that have to be checked and set before this would be the course of action.