I think it could be handy to have the ability to pin an entry to the top of your timeline view so it's always there - think how subreddits on Reddit can have pinned posts that always display at the top.
I can think of a number of uses for a pinned post - as a reminder of something, as reference, even just a way to keep notes.
In my case, I recently had to make myself a rating guide outlining what I consider to be a 1/2/3/4/5 star day, since I realized I often rate my days inconsistently, and having that pinned for reference would be nice. I also use emojis as tags and it would be nice to have those listed out as reference as well, as sometimes I forget what each emoji tag is meant to represent.
This might be a very niche thing that isn't needed by most people, so it may not be seen as necessary. Just sharing a thought because maybe others would find such a feature useful as well 🙂