What onsessionstart() do in coldfusion?

The onsessionstart function in Coldfusion is used to initialize the session scope data or session-specific application scope variables. This method can also access the variable scope if the application.cfc file has an onRequest method. It doesn’t return any value and runs when a session starts.

//Syntax
<cffunction name="onSessionStart" returnType="void">
...
</cffunction>