I noticed alot of our forum members have a hard time understanding and correctly expressing their offsets, so here is a visual aid.
The reason I made this is alot of people tend to think that if they have a wheel that has an offset of 25 and they add a 5mm spacer to it that it becomes 30 offset. What you are doing with a spacer is pretty much moving your hub surface further into the wheel, which makes it a lower offset by however many MM the spacer is.
The generalization you can make from this is that when the offset raises the wheel tucks more into the wheel well and when it decreases the wheel moves out towards the fender.
I hope this helps us visual things a bit better.
I appologise about the paint drawing as I felt like drawing it myself because I am bored at work