Most of the time, Aspose.Word produces documents that are smaller than documents produced by MS Word because we always do a full save, don’t store any undo or other buffers. This is even regardless the fact that Aspose.Word always stores all text as Unicode, whereas MS Word uses Unicode only for text that needs it.
The only time documents produced by Aspose.Word might be bigger than documents produced by MS Word is when you insert metafiles using DocumentBuilder as I don’t think we compress them yet.