The Additional comments and Work notes fields are the two Journal fields that are present by default on the Task [task] table (and thus, on all tables that extend the task table):
By default, the Work notes field can be updated only by users with the itil role, whereas the Additional comments field can be updated by any users. This creates a separation between notes that are meant to communicate back and forth with the customer, versus notes meant to log work or serve as technical information that shouldn't necessarily be exposed to the user.
More on Journal fields in the next section.
