The activity stream combines record updates and journal entries. Work notes hold internal support communication. Additional comments can be used for customer communication, depending on the application's configuration and notifications. Confirm the audience before writing anything sensitive.
Journal entries append to the activity history. They don't behave like a single text field that you replace each time. Keep an entry specific enough for the next support person to act on: describe the observation, test, or next step. A note saying done doesn't explain a repair. The simulator keeps journal text in order, so your check must include earlier entries when a task starts with history. Editing a description doesn't create the same kind of record as adding a work note.