[Xslt 3 Start] Use case for Function Call Invocation

Hello !

Reading the recommandation, I was not able to imagine a use-case for 
Function Call Invocation 
<https://www.w3.org/TR/xslt-30/#invoking-initial-function>[1].

Recommandation only speeks of raw result, and 2.3.5 section does not 
mention a "starting environment".

Saxon implementation does not provide a command-line way to start a XSL 
with a function call invocation ; there is only an API method to do so. 
And in this case, a XDM value is return.

Could W3C Xslt group members explain the motivation of such a starting way ?

Does someone has a real use-case of this invocation ?

Best regards,
Christophe

[1] : https://www.w3.org/TR/xslt-30/#invoking-initial-function