Whenever there's a significant difference in the outer diameter of of one tire in a set of four, it adds to the work that the differentials have to do to compensate for that difference. Because our Subarus are AWD, there are three differentials; front, rear, and center. The axle differential would get a workout equalizing the right and left tires, and the center differential would get a workout equalizing the front and rear.

This issue arises in long-term use, as differentials are always compensating for different tire rotations, especially in corners. They're designed to work. With an odd sized tire, though, the diffs are working in straightaways as well. Bottom line, the added stress shortens the life of the differentials.

The problem is compounded in cars with a limited slip type of differential because there's a friction component to decrease the differential's natural desire to send power to the tire with the least traction.

As far as messing up cornering, well, maybe. The car might pull if you put the tire on the front. There's also a difference in traction between new tires and old, which can change the understeer/oversteer balance built into the car.

The real issue, though, is the differentials. My own rule of thumb: If my tire is about 25% worn, I'll replace two. If it is more than 50%, I'll definitely do all four. Those percentages might increase a bit if it was a 2wd car.