OK,

In SQL 2012 you can have a read-only copy of the database - which you can use for SQL Reports,

in this case you can use READ UNCOMMITTED or skip it altogether (according to Gail).

Normally you would use READ UNCOMMITTED in stored procedures of SQL Reports if they point

to Application server database - NOT to impact performance of the Application you would not worry too much about the totals that are slightly out

(I know best case scenario is not to run reports from Application server databases - but in reality not all companies can afford a data warehouse or data warehouse skilled employees).