Based on an admittedly small observation sample, I think that people who maintain TODO lists have much less "free time" than people who don't. Some even maintain their TODO lists in the lack of other work.
Personally, I don't maintain a TODO list, and I manage to finish all my work in time, and there's also some time left to have fun :) I do maintain a (small) text file named "TODO", but it contains very low-priority stuff, which can be done anytime (tomorrow or in a year; doesn't matter). And all of the things there are longer-lasting things (e.g. reading a book). It should really be called "REMINDERS" instead of "TODO, but "TODO" is shorter :).