We like to say that you can't plan for where you are going without reviewing where you've been. Also, if you don't spend a little time thinking about the entire last 12 months, it's easy to just dismiss it as "well there goes another year with nothing done".
This is because of the cognitive bias of "recency" which basically means that humans have bad memories and favor recent events or historic ones. And if you're like us, the last couple of weeks have not been as "productive", as the 50 before it. The last weeks of the year are wonderful in many ways, but unless "drink egg nog" is one of your goals, you might not have "done" very much.
Of course, sometimes that's the whole point, and to that we say "huzzah!"
However, once you are ready to start "doing things" again, an annual review puts everything in perspective and is a fun way to reminisce about your year.