I find the use of inequality in auto layout tricky (and hard to grasp) because two-constraints per dimension no longer applies. For example, if I want my UIView to be at least 200 pixels wide and centered around X and Y, I still get ambiguous constraint because auto layout cannot figure out how wide the UIView should be. If I specify an additional, exact width constraint, doesn't that defeat the purpose of setting the inequality width constraint in the first place? How do you use inequality constraint in practice?
You would use the inequality with some other constraints at a lower priority. A static width wouldn't be very useful in this case, we're looking more at intrinsic content sizes (so the hugging and compression priorities). So you can have a view which has a minimum width but grows to accommodate additional text for example.
If you don't have this intrinsic size then the size is ambiguous because it could be anything > 200 and there is no correct answer.