This report is very useful if you want to view summary level information across multiple email campaigns, during a specific time frame. For example, this report would be helpful if you wanted to compare the open rates of 10 different email campaigns that ran from December 1 - December 31.
The report produces a downloadable excel spreadsheet that looks very similar to the report summary screen in the product. Once you download the Excel report, the data can be modified to suit your requirements, i.e. sorting various columns, deleting campaigns that you don't need to include, etc.