I'm mostly using it for world building and after session notes. The second part is also used when I'm a normal player and not the GM.
I use second hand paper (as in the back of flyers, old Calendar used months etc) for note taking during play, I find it takes less concentration and l can do it more freely during play
For planning and session prep I use Obsidian, since I can also use that at work, and you never know when inspiration will hit.
Also of note is that I use CL normally writing in Spanish and it works great.