Until recently all carts came with no bushings. As you can see here, they tended to dent the hull bottoms (though most of the dent would come out later) and toggle a little in the scuppers.
In some of the hulls tennis balls would shift the load to the stronger scuppers. But with the older, short cart legs some of the scuppers became too deep for the cart to extend through the hull (a primary requirement). On others, like the Outback the balls were just not enough:
The availability of cart bushings represents a great improvement for the carts. All new carts include them and older carts can add them for about $10. Because the bushings are hard plastic, they only have a single point of contact. So in models where the cart cross bar still can contact the hull bottom (with bushings installed), the bushings are set for a three point contact to help distribute the load and stabilize the cart like this:
The new wide wheel base carts (now standard) have longer legs so there is room to add tennis balls to the bushings for better load distribution in most cases and still have the cart fit properly (as shown previously).
In other models the bushings lift the hull away from the cart as with our '08 Oasis. This is still an improvement (if your cart has long enough legs).
But in hulls where bushings lift the hull like this, If I have to choose between bushings or balls, I still prefer the softer, load distributing tennis balls.