I list my most common usecases here [0], but if I had to name just one thing, it would probably be promnesia [1]. It's an extension that I'm working on, with the purpose to actually use all this information and integrate it in my browser, like a remembrance agent.

[0] https://beepb00p.xyz/hpi.html#usecases

[1] https://github.com/karlicoss/promnesia#demos