I was looking for a way to parameterize the value for a filter criteria field on a number of reports.  That way I would not have to edit a large number of reports whenever the filter value changes once a year.  I used a Salesforce Custom Label and passed it in the report URL using  '?pv0={!$Label.Financial_year}.  Now whenever that value needs to be updated, I change the value in the Custom Label and don't touch the reports.