Even if the police can not do a lot about it, the report will end up in some statistic. That statistic in turn might lead to more resources assigned to the issue, either directly (crack downs, recovery squads, whatever) or indirectly (programs to get people into proper jobs, help for drug addicts, whatever). This might also serve as a control for indirect measures.

People often demand decision makers to make good decisions, and to look at the data. But then we need to apply that data to them.