Random plugin question?

Hi,
I'm learning how to write notes from a plugin. Therefore I studied the "random" plugin.
What I just don't understand: where come the rest(s) from, it inserts at the end of each measure?
If I remove the cursor.next() commands, no rests will be created.
Obviously addNote() advances the cursor and cursor.next() advances it too. In a real example: when would I do cursor.next() and when not?

Best regards

Michael