The Hootsuite Analytics overview automatically analyzes two time periods: the one you select, and the corresponding length of time before that. For example, if you select the last 7 days, the overview will automatically pull data from the previous 14 days. Why would this be a benefit?
to put your analytics results in a more historical perspective
to add fullness to your metrics reports
to provide an estimate of future trends
to make it easier to generate ROI reports for key stakeholders
this is not a feature of the overview module