Some big types of reporting can easily be told apart. Just as an example, a first type is targeted to monitor, measure and hopefully improve the software or systems processes in place. A second type is targeted to management outside the strict IT scope.
The first type can then be divided into categories, such as Capacitity-related, Performance-related, Cost-related, etc. while the second type could contain progress reports to project stakeholders, SLA compliance reports to service clients...
Some of the first ones are hopefully going to let the organization IMPROVE its future performance, decrease its costs... while some belonging to the second group might prove useful to PROVE performance or justify further investments. for instance.
A possible recommendation would be to build s simple list of all the reports currently being generated, add a few reports that someone is requesting, and finally throw in a few more that sound useful even if nobody really asked. Then try to find out what are the benefits of each report. Which decisions would be easier because of the report availability? Who is going to have an easier job because of these data? What kind of trends can be spotted thanks to them? A simple approach can be limited to removing the reports which are obviously useless. A more complex approach might also try to 'weight' usefulness and compare it to the effort needed to generate or populate the report, and then use the results to prioritize.
In some organizations this exercise can end up showing an alarming number of reports which nobody really needs, and keep being generated just because 'they were produced when I joined', or 'everybody has them'.