It could be a chassis tuning specification. For example on road track prepped cars, to achieve neutral handling. How? Well if you put a "proper" sized tire on a rim, the shoulder of the tire forms a relatively squared corner. This can yield maximum grip numbers, but can also make the traction limit less predictable, and be more prone to snap loss of traction.
However, if you use a slightly narrow tire on a rim, it rounds off the shoulder. By doing this, you can get a much more predictable break away at the limit of traction. Also, with changes in suspension geometry you can often get this more forgiving setup without losing any maximum lateral acceleration while cornering.
If you don't believe me, go talk to the Japanese track attack race teams where they essentially get 1 lap to go around it as quickly as possible. I believe even Boss and Cusco, famous modifiers of WRX's and Evo's even does this on some of their cars. They even do this on some of the cars in the Toyo race league where a bunch of almost stock cars ranging from BMW 3s, to Acura TSXs, etc race against each other on Toyo street legal rubber.
***FORGOT TO ADD***
Also, by having this incorrect offset on your car, you have now essentially increased your track, without similarly widening the track for your hub. As a result, your wheel bearings are gonna take a beating. Having your offset off by an inch is PLENTY enough to put unusually high loads on your wheel bearings even under normal straight line driving.
It's all part of the ghetto low-rider life. I kid
So they get wide wheels and put thin tires on them?
Seems like they are just asking for trouble .......
or too cheap to put real meat on their rims.