1. It doesn’t rely on expiry deadlines to provide the motive power.
2. It’s much more immediate in producing the right task at the right time.
3. It doesn’t leave you with an indigestible chunk of difficult tasks which have to be done or lost.
4. It deals with all tasks on the same basis.
5. It produces a much greater degree of psychological readiness.
6. It’s easier to keep the entire list under control.
7. It doesn’t allow tasks to build up resistance.
8. It works equally well with a short list as a long list.
9. It’s easy to extract a shorter list (e.g. for travel) and use the same methods to process the shorter list.
I’m sure I can think of some more if I try!