Low vs. Mid vs. High Offsets?

[240fluke]

What is the real difference when it comes to these Low, Mid and High Offsets? It should be the depth of the dish on deep dish rims right?

So how come there are rims that have something like a +15 offset and it is a mid, while the same type of rim has a +11 and is low or +17 and is high? Or rather something more along the lines of a -7 high and a +11 low offsets or +47 low vs. +41 high? How would someone even go about picking the type of rim they would want when the selection for offsets is so drastically ranged like this?

Do these offsets that are low mean that the dish is like 70mm, while a mid is 80mm and a high is 90mm or do these offsets mean something different?

If that is the case then it would mean something like a high number (+45) with a high offset would have the rim more tucked up in the wheel well while having a real deep dish to it, while a low number (-7) would push that rim out farther from the car and still have a real deep dish on the rim as well? Is that how these work?

If this is the case, then why would you choose a low vs. mid vs. high offset style rim? Caliper clearance? Maybe Coilover clearance?

Tim '95 SE