I used to have a love-hate relationship with lists. Here's why.
Scenario 1: I know that I am going to go grocery shopping tomorrow. I make a mental note to buy some plastic forks for my desk at work.
Tomorrow comes. I go grocery shopping. I forget to buy forks.
Lesson: Alway make a material note of things that I wish to remember, not merely a mental note. If I make merely a mental note, I will forget.
Scenario 2: I know that I am gong to go grocery shopping tomorrow. I realize that I need some plastic forks so I add "plastic forks" to my written list of items to pick up at the grocery store.
Tomorrow comes. I bring my list but never look at it until I reach the checkout line. I discover that I bought everything that was on my list.
Lesson: Never make a material note of things that I wish to remember; make merely a mental note. Material notes are redundant and reduce my efficiency. The time spent making, carrying, and checking material notes, could better be spent doing some other productive activity.
Scenarios like 1 and 2 above have been played out in my life many times. It always bothered me that if I didn't make a list I needed one but if I did make a list I didn't need one. It seemed almost as if there were some Cartesian malicious demon messing with my life preventing me from drawing useful generalizations from my list-making experiences.
Obviously, I have been drawing the wrong lesson from scenario 2. The reason I remembered to buy the forks in scenario 2 was that I made the list. I didn't need the list once I got to the store but the list was not superfluous. There is something about materially externalizing mental events that makes them easier to remember. Saying them out loud, writing, drawing, using color, using motion: all of these sensual experiences make an event memorable in a way that mere cognition (thought) does not.
The same lessons apply to GTD. Even when I am not reviewing my lists, I am more aware of what my commitments are and I am less likely to let commitments fall through the cracks by the very fact that I have put them on a list.