I use them at work - when in the hospital, to jot down notes and to-dos throughout the day to help me document electronically later. When I'm in my research role, I have tons of meetings (many via Zoom). I have a big Leuchtturm1917 (A4+) notebook that I use to jot down notes, which keeps me engaged, and also to work out ideas / write out math or pseudo-code.

Outside of work, I will sometimes write passages of poetry or prose to try to improve my handwriting or check out inks. I'm giving the journaling thing a try at the moment though it's not something that I've done regularly before.