Well, body roll is never a good thing. What you are thinking about is chassis roll. On carpet, less is usually better. What it is good for is low traction. What happens is this: pretend you are riding in a full size car. When you go around a turn, the car leans toward the outside of the turn. Well, that puts more weight on the outside tires. In R/C, that translates into more bite on the outside tires. On dusty parking lots, I have run as light as 25wt oil and green and silver springs on my TC3 (some of the softest) to make my chassis "roll" more. It puts more of the weight on the outside tires and makes the car track better. On carpet, traction is usually not a problem. The reason for not letting it roll is because it slows you down. When the car rolls, it unweights the inside wheels and in extreme cases can cause the diffs to unload and tires to spin. Increasing the chassis roll may suit your style of driving, but if your car is hooked up now, don't mess with it.
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