Detect file units and import as 1FileUnit=1UnityUnit, otherwise it will import as 1cm=1UnityUnit.
This setting is used only for .max files. It was introduced for backwards compatibility: there is a bug in some FBX 2011 plugins - they fail to pick up file units and export everything as 1unit=1cm. We fixed that problem by setting the units manually, but that breaks projects which were built with FBX 2011 plugins already, so useFileUnits was introduced as a solution. Set it to false if you want to default to centimeters in FBX exporter.
See Also: isUseFileUnitsSupported.