When I was growing up I couldn't afford a computer so I would write Basic on paper and save it for when I could get to school or somewhere else with a machine, then type it in. I definitely feel it made me a stronger developer as I had to "think like the machine" a bit more than when receiving immediate feedback while composing a program. The programs I was writing were insanely simple but I feel it was still a good exercise.
My handwriting was nowhere near this nice though :)
I am always reminded of the first chapter of Lev Manovich's The Language of New Media where is writes about growing up in the Soviet Union and he took two years of computer programming without ever touching a computer. At the end of the course he got to use a computer once where he put his program into the computer and it doesn't work because he typed Os instead of 0s.
My first programming class was in high school in 1980. The teacher, Mr. Schultz, invented a pared-down, abstract assembly language he called SIMPLE (Schultz's Imaginary Machine Programming Language for Everyone). We spent the first month of class writing out solutions to programming problems in SIMPLE on paper before we ever touched a computer. And even then, we only had the one machine, so we had to take turns on it. We coded our BASIC programs on paper and checked them as thoroughly as we could to maximize the effectiveness of our precious time with the actual hardware.
I really like finite state machines, for sketching out a basic program flow.
Nothing as complicated as big formal UML diagram, but IMO a quick sketch of a program as a 'grid' is a nice way to visualize and quickly iterate on logic flows.
My handwriting was nowhere near this nice though :)