Making diagrams and mock-ups with Excalidraw and a USI 2.0 stylus. For me it's a whole new way of creating things. None of my other devices can do it. (Screenshot)
It's a superior device for showing people stuff around a table. Here, hold this screen, look at this website or whatever.
It's a superior device for uni-tasking. Feels less distracting than a desktop OS with a bunch of windows open.
For a writing session with a physical keyboard, you can stand it up in vertical mode, see more lines than a laptop, at a comfortable column width. I'll use a bluetooth mouse too. I generally write with Joplin. (photo)
Walking around with a nice screen I can use without any furniture. At conference-like events, having the schedule and some notes handy.
Reviewing photos I took with my (GrapheneOS) phone. "Keep this one, delete this one". Syncthing makes this easy.
I've done a little programming on it with an external keyboard/mouse and Gitpod (basically VS Code running in a browser), it's a bit glitchy but okay.
Music while working. Somehow, having music control on a device off to the side of my computer keeps me in the flow of work a little better.
Pinching around maps with OsmAnd. Using ChatGPT. Wikipedia. Reading blogs. Watching videos with NewPipe.
My data synchronization strategy is basically: Firefox Sync, GSConnect (i.e. KDE Connect), Syncthing, DAVx⁵, and Joplin backed by Dropbox (but end-to-end encrypted).