Basically, weekly reviews are tactical, where you can mostly mechanically prioritize the upcoming week and clear out your inboxes. Monthly are more strategic, where you take a wider look at the status of all projects, consider modifying, canceling, or reprioritizing them. And annual reviews are the same thing but addressed at the highest level of your life; you might think of it as a formalization of New Years Resolutions.
Since adopting a schedule of these reviews I have felt much more in control of my projects and work, and the time investment is about 1 hour a month to do.