sticky pin use

Just a curiosity…When the notification window is showing there is a sticky pin in the upper right hand corner. What is that pin to be used for?

If you mean the popup windows of panel applets: if the pin is activated, the pupup stays open even if it looses focus.
Useful e.g. to keep the calendar open while writing some text in an application…

Normally the popup would be closed again if you click on an application window e.g.