Send note by default
This is an option, that turns on checkbox Send note by default. You won't need to check it every time manually. In orded to use it, go Administration -> Helpdesk and check the field in.
When you edit the issue, you will notice that Send note field is checked in.
If Send note is not checked, only Redmine users involved in this ticket will see the notifications about answer (it can be used if you want to have private conversation with team members without notifying customer). And if this checkbox is checked then the comment text will be sent to customer - helpdesk contact - as well.