Roles and groups allowed to be set as watchers
Project Roles, Groups, email addresses set as watchers of projects or issues.
In-app notifications delivered to users
Project level configuration as set in the Configuration page of the app.
User preference of issue events to get notified on. This is set in the Project Watches page
A Jira Project's Notificaiton Scheme used to deliver in-app notification.
This is set in Project Settings / In-app Notifications
Users' project watches setting as set in the Project / Watches page
Users' watch preferences as set in the User Profile Menu / Watches screen