Audit PowerPivot and PerformancePoint - are they being used?

Hi,

I am doing an audit of SP2013 environment. I can see the service applications and configuration for PowerPivot and PerfPoint are all set but I need to understand if they are being used at all.

My understanding is that you can have data connections (e.g. from Excel) to external databases and display the results/dashboards in SharePoint.

Is there a way to find if those services are being used? e.g. do I need to find specific files like data sources or data connections? what type of files would I need to look for?

Any other tip welcome