Author here. Two reasons I chose an immediate mode UI framework:

1. Latency. A click paints on the next frame, because it sidesteps the stages of a retained mode UI: there's no dirty-marking, no layout and paint passes scheduled for later, no cached visual state that can be stale.

2. Simplicity. The UI is a plain function of app state. There's no retained tree to keep in sync and no invalidation bugs: mutate the state and the next frame shows it.

Yes, the drawback is that you have to watch what a frame costs, but it doesn't repaint at every frame. It paints on input and you can schedule repaints yourself. Fastpotify sits at zero CPU when idle, asks for a few frames a second while a track plays, and runs at full rate only while you scroll.

“Claude, why did you use an immediate mode framework?”