You may be assuming that GTD sets the level of granularity for a project. But it doesn't. I'd say that if the next action for your project is so obvious that it's not worth writing down, then you may have defined your project in more detail than you need.
Originally Posted by supergtdman
For example, an experienced baker might have an action "Bake chocolate cake" inside a project "organize Joan's birthday party". For her to break that down into, "buy chocolate" and "look up recipe" and "wash springform pans" is a waste of time; the tasks are instinct for her, and for things like the chocolate, she probably has some system to make sure that she always has supplies, elsewhere in her GTD system.
But a novice baker might need a separate project for baking the cake, one that includes actions like "ask Anne for an easy cake recipe" and "find a source for Callebaut chocolate online" and "find online video on how to separate eggs" and "find out what a springform pan is."
For your "bought Macbook", _you_ don't need intervening tasks. But someone who doesn't know much about computers, doesn't even know what he's going to do with the thing, probably does need intervening tasks, like "Ask Joe to lunch to talk about computers" and "Find out what all those system requirements lists mean" and "Ask Joe why he said to always get the extended warranty on laptops."
And someone who knows plenty about computers but whose days are very crowded may need tasks just to keep the "buy computer" project on his radar so that he doesn't suddenly find himself with a project that requires a faster computer and a six-week backlog on the computer he wants.
On writing the book, if the book requires that you do a lot of research about, say, family-owned farms in rural Tennessee, and you conclude that you need to do that research _in_ rural Tennessee, that's not something that you're going to wake up one day and spontaneously do. You'll need to choose dates for the trip, get plane tickets, get lodging, and take the trip. You might need to remember to bring your camera and your mini tape recorder for taking pictures and doing interviews.
You might need to make appointments with the people that you want to interview. Those people might be hard to reach; you might need to call around every week for six months before you can get a group of interviews set up for the same week.
And if you do all that and come home with your research, then realize that you also need to go see the Hermitage outside Nashville, and you need to get on a plane again when you could have just organized your trip to use the Nashville airport, you'll be rather annoyed with yourself.
To me, that involves actions and processing and prioritizing and planning. It's up to you whether your Next Action is a simple "touch base with interviewees" or a more complex "Check interviewee list." followed by "Create call list." followed by "Call Joe." But they're all Actions.