Imagine one day you did something on your laptop two months ago and you want to find out where you did it. If you don't remember, it will do it for you. If you want a detailed daily summary of your activities, it will do that for you. If you want to summarize a meeting or your university lectures in detail, it will do that for you. People were afraid of this technology because it wasn't private, and that's completely understandable. Now, imagine having the same technology but completely local. All your data would remain confidential and encrypted, and you could ask it any question about your digital activity.
I use an app like this that I built myself. It's great to recap yesterdays work for a standup, or the previous month for a retro. Those are my most regular usages of it, but every now and then I am able to use it to recall something I definitely forgot about ("who was that guy in the meeting" or "which slack channel was that again").
