As in economics, there's a law of diminishing returns when sizing rims and wheels for your car. When you hit the point of enlarging the rim and wheel to where the wheel well is nearly filled, certain things happen such as the inability to steer the car very well, the inability to accelerate as well as you had thought and an inability to have the braking control you thought you would have.
When you look at the potential size of wheel and rim combos for a car, you usually start with the base tire that comes with the vehicle. Let's say it's a P195/65R16 88Y. This tells us the tire is passenger car tire that's 195 mm wide and about 117 mm wide (the aspect ratio). It also tells us the tire is 16 inches and will have load ability of about 1,225 pounds or so, and that it can run at speeds over 130 mph. For most people that would probably be good enough.
However, this is, admittedly, a minority that things if I can get this much from X, then X+1 will get me more and so on. The only thing that will happen when they are finished installing their oversized wheels and large rims is that the tires will rub the wheel well; the car won't turn safely through its entire arc; the brakes will likely fail because the wheels won't roll as they are jammed up against the front of the wheel well and the handling is severely compromised.