Why? Because it's faster to write a few paragraphs about how a game play feature will work, visualize it in my head, play it through in my head, look for problems in the visualized gameplay, revisit the paragraphs describing the gameplay, and rewrite until I have a very clear picture of how the game mechanics should work. An hour invested in thinking through the game play before writing code saves me ten hours of coding & rewriting after I discover the game play design flaws. I'm very happy when I write out a long game play element, revise and tweak it, discover it sucks or is not feasible, and then toss it aside, all before writing any code.
By the time I get to coding time, I've got a very clear and trimmed vision of what I'm trying to accomplish and how I'm going to accomplish it. If I don't, then I sit back and think some more.
Here's another productivity tip: Take periodic mental notes on what you're working on. Ask yourself "Is this significantly contributing to the project?". You may find that you're wasting time on polishing art assets when you should be prototyping instead, playing games, or surfing internet forums....like this one...for hours on end... hey wait a minute, I'm wasting time right now when I should be working...
