I dont think any complex plan should be planned in your head. But drawing diagrams, sketching components, listing pros and cons, 100%. Not jumping directly into coding might look more like jumping into spec writing a poc
It shouldn't be your only source of a plan as you'd likely wind up dropping something, but figuring out how to jiggle things around before getting it 'on paper' is something I've found helpful.
Personally, for me without writing or sketching I cannot think complex things: as in complex logic, constraints, etc.
I guess this is topic too abstract, so we can read into it different things.