This tool automatically excludes all duplicate objects, i.e. objects that are on top of each other and have identical geometry.
This tool is useful when the model author has by accident pasted multiple copies of the same object into the model, e.g. when copying objects from one building storey to another. This would cause for example duplicate quantities on quantity take-off. By excluding the duplicates they won’t be included in the export and thus have no effect on any consequent analysis.