Call hierarchies, more info needed

When I read the 3.16 information about call hierarchies, I am left scratching my head. Is this mechanism all about finding out who calls or is called by a symbol (the cursor is placed on)?

The first question that pops up is how would this work in a functional language where a caller or callee is a piece of runtime data?

Second question is, given a cursor on the middle of the "print" call reference of the proverbial hello world program, what should the various call hierarchy requests do?

Might be very useful to provide examples or cite references to further explain what the LSP designers are trying to accomplish/achieve with this mechanism.