The absence of a datum in XML can be expressed either by omitting the element (minOccurs="0" in schema) or by setting it to xsi:nil="true" (nillable=true in schema).
Using minOccurs=0 seem altogether cleaner and more consistent, and it doesn't require the XML to reference the XSD namespace. So what is the benefit of nillable?
Best Answer
nillable is in the spec because the XML Schema WG had a number of members who saw the world in SQL terms and wanted an explicit equivalent to SQL's null values. It's totally unnecessary in my view: just ignore it and don't use it.