The middle click brings you shortcuts to common action. The actual action depends on the application.
To perform a middle click do a 3 finger tap.Common middle click actions
Windows Taskbar:
- Click on an icon for a new instance of the application.
- Click on an app preview icon to close the application instance.
Web Browser:
- Click on link to open a tab in background.
- Click on a tab to close the tab.
- Click in the page for pan mode.
- Click on a bookmark folder to open all bookmarks in a folder at once.
... to be continued.