In this section we will talk about Wheel Offset, and how it effects perfomance and other factors of your vehicle. Lets start with the difference between Negative and Positive offset. Positive offset is how most factory wheels are designed. The wheel center is moves the wheel closer to the vehicle, therefore moving the tire closer to the vehicle, helping to tuck it under the fenderwell. This means the wheel rotates on its axis.

Negative offset is how most aftermarket wheels are designed. They move the center of the wheel away from the vehicle. Therefore, moving the tires away from the vehicle, and increasing the turning radius. Rather that spinning on its axis, it swings on its axis. There are several inherent flaws with this, while they may be unavoidable. Increasing the offset puts more leverage on the lugs, which means you can break them easier, but it also increases the stance of your vehicle to help keep it more stable. The swinging affect means more lift is needed to avoid rubbing.
Here is a real world example:
On a 1988+ Chevy Fullsize, you put on a 6" Trailmaster Lift, which requires you to use Negative offset wheels. You put on 35" X 12.50" tires. Your large tires swing back and forth and rub the outer fender, therefore you need 2" more lift to clear these tires.....
On the same 1988+ truck, you put on a 6" Pro-Comp Lift, which will allow you to use the factory positive offset wheels. You put on the same 35" X 12.50" tires. Your wheels spin on their axis, inside the fenderwells, and you experience no rubbing, and no additional lift is needed.
Reasons to use Positive offset wheels:
Less leverage on the lugs and steering linkage.
Keep tires tucked under fenderwells.
Reasons to use Negative offset wheels:
Move wheels away from vehicle, when tires are rubbing frame during turns.
Increase vehicle width, making it more stable.
Some people like the "deep dish" look the wheel offers.