Each user can configure filters for notifications.
Each filter is a jql request and a set of events.
If a task change falls under this filter then the user will receive a notification.
Event sets are set by administrators in the menu.
{baseUrl}/secure/jibrokViewAllEventSets.jspa
The set may include various system events, changes in fields, statuses. There can be a lot of events. The user (not the administrator) most likely does not know all the features. Therefore, administrators pre-configure sets of events and describe them. Users then choose their own suitable set of events.