Many organizations work in environments where they need to produce documents that contain both Imperial and Metric dimensions. AutoCAD has had the ability to do this easily for many years, but Revit just recently gave us the ability to easily show both methods. Since it has not been available like this for very long, many Revit users are not aware of this important feature.
Since the Revit 2014 release, you can display Primary units and Alternate dimension units for both the permanent and spot dimension types. This feature allows you to simultaneously display both imperial and metric values in drawings as primary and alternate dimensions.