3ds Max has two unit settings, System and Display, that can create conflicts when you try to exchange data between 3ds Max and MotionBuilder, Maya, or Revit.
If they are set differently (for example, inches and centimeters), the 3ds Max System and Display units settings do not create issues as long as you are only working within 3ds Max. However, MotionBuilder and Maya use centimeters, and Revit uses feet/meters, so conversions might occur each time an FBX file is moved between those programs.
Generally in 3ds Max, changing the System Unit Setup is discouraged as it can create confusion. But for the purposes of file exchange and interoperability, altering 3ds Max System Units is necessary as FBX files do not take 3ds Max Display units into account. Consult the following sections for a detailed explanation of the scaling problem.