Why taking the trouble of writing stuff about how you do stuff? Isn't it a nerdy thing to do? Doesn't madness lie that way?
Well yes and no. As with most of what we do, it all depends on what's the underlying motivation. Regarding this science/art of how-we-do-what-we-do, I always find healthy to remind myself that notes, To-Do lists, calendar plans and all the like, have a main motivation: getting us to the fun part as quickly as possible.
Human brain has a wonderful plasticity; it quickly rearranges itself to do things completely different. We can be at one moment planting a rose and the next one trying to appease a crowd.
To take full advantage of such plasticity, it's a good thing to remember that the change of activity has a cost, in terms of effort --the tiny wheels inside the brain must be replaced, the microscope lenses leave place to the telescope...- By creating guides for ourselves, we facilitate that change of dies. Those guides don't need to be groundbreaking. In fact the simpler they get the better ("The goal is making things as simple as possible, not the other way round", said Taiichi Ohno). A mark on the floor, three words on a piece of paper, a colored sticker on a cable, a quick shot of a console taken with the cellphone, all can become unspeakable acts of kindness to our future self.
By creating those guides, we can move on to other part of our diverse, multidimensional life, and be sure that we'll find the way back easily later. Someone in the GTD forum called action lists 'stakes on the ground'. They tell you how far you got, and where to resume the game tomorrow.
I also find useful to compare them to those opening teasers you get on some TV shows, which brief you in a few scenes on on what happened previously. Our brain comes from car mode, grocery list mode, dialogue mode, or having a shower mode, and must be quickly and effortlessly tuned to audience mode: "I can't wait to get to Caribbean/oh look that engine is burning/The teams have given up but I know she survived". Oh, yeah, I remember now, I'm ready to go; so what's next?