Excessive wear on brake pads is a sure way to ruin rim sidewalls. During the winter months when roads are wet, brake pads seem to dissolve before our eyes. The road grit and water combine to make an abrasive that wear out the brake pads more quickly than during dryer riding conditions. Once the pad wears down considerable, the stopping power of our brakes plummets. Another casualty of excessive pad wear comes once all the rubber material is worn away. This exposes the metal base to which the pad material attaches. At that point metal on metal friction occurs every time you apply the brakes. The result is the destruction of the rims sidewall. Once this occurs the rim wall will lose its structure and potentially blow apart from the back pressure on the tires.
Keep an eye on your brake pads and replace them often. They are much cheaper than new wheels.