The first and most exciting part of this is the ability to have a 'day in the life' consolidated ledger of our activities on device, across all app experiences. The ability to log our lives and add our own thoughts on top of it is important for self-reflection and for the many moments we want to recall using temporal cues and in context (I remember I was talking to Joseph and then saw a really cool webpage).
A lot of the time the act of journaling is writing about the activity that has transpired on/through our devices (who we spoke with, what we did, etc), yet currently there is no affordance to link these together. We may add a note in a calendar event to remind ourselves of what happened, or rely on our memory, but just to look back at our day we have to cobble together a mix of calendar, notes, messages, etc; it's all a very disjointed experience.
A consolidated journal/ledger of the day with the ability to write atop it is essentially the user-facing version of what a future AI assistant would see and present to users. A good assistant would not just do tasks but solicit our feelings and attune to us, which is essentially 'journaling' when brought into UI form.
This whole product is frankly quite a bit overdue.
The second value-add of this idea is tying journaling closer to Health. Health journaling is essential to managing chronic conditions, as its value is primarily retrospective discovery of trends. There's a lot of sub-par health journaling solutions out there, and none do a good job weaving themselves into the context of Health data. I hope to see this use case in this initiative.
The history of our usage of devices has always remained a largely unexplored area of computing, and one of the major divergences between how people see the world and how computers present the world to us. Bringing history back to us in human-consumable form is important to get this sense back. The only other initiative that I see taking on this need is rewind.ai, which is quite exciting and I'm guessing is on Apple's short list of potential acquisitions.
Finally this seems like the next step in the feature trajectory of adding context to our device usage. The first feature in this trajectory was Apple's Shared with You framework [1], which is about adding contextual data tags to activity (E.g. seeing a webpage in Safari showing at the top that it's shared by your friend Joseph, which reminds you of why its relevant).
(FWIW I've spent the last year designing an OS for a new tablet platform with journaling as a central experience)
[1]: https://developer.apple.com/documentation/sharedwithyou