Staggered wheels and tires have become popular both for Original Equipment and aftermarket packages.
The most common stagger is to have the wider tires on the back and the narrower ones on the front. This is perfect for rear-wheel drive cars, especially those that have a mid- or rear-engine configuration. With all the weight and power out back, they need a much bigger rear tire.
On front-wheel drive cars, which already tend to understeer, putting a wider tire on the back is a detriment to handling. 90% of the braking, all of the power delivery, and most of the weight-bearing is being done by the smaller tires. The overworked front tires give up first when pushed, and the car wants to plow straight ahead, inspite of the steering input telling it to turn.
Enter the Pontiac Grand Prix GXP: it has staggered tires, but the front is the wide one. This looks a bit odd, but it is the only way that staggering makes sense for front wheel drive. In a triumph of logic over style, the wide Pontiac tires are on the axle where they are doing the most good.