When the Site Picker is defined in a page with Site Analytics & Changes audits, it allows the user to select a specific site to filter the two web parts with a specific sites versus the default site defined in the web parts.
How to use it :
Click on the Site picker on a page configured with Site analytics
Type a site name ( In our exemple, Gamification )
Site picker will found a site based on the words you type, select it
The selected site will be displayed in the Site picker and the site analytics and Change audits webparts will be updated with the site's data.
Deployment and prerequisites
Site picker is available on the Intranet part of the webpart catalog