Wheels for a duster offset and backspace

I still don't understand why a person would worry about offset, the back space is what really matters for wheel fitment ,if the back space aint right , it wont work if ur pushing the limit on wheel/tire size.
I have to have a 3 1/2" back space with my rear end length, and tire / wheel combination, I could care less about the offset in mm measurements.???????

I'm not going to tell you what you should care about but take a few minutes to try out this calculator and see if it changes your mind.

Custom rims, wheel tire packages