Reviewing is what I call remembering and memorizing a dream while lucid in a dream. It's a recall boosting technique.
I like to review multiple times in each dream if possible--usually after I've been in one for a while and notice I should review by now to be safe, while I'm between dreams, or early in a new dream. I also like to review during LDIW, when I'm awake but haven't opened my eyes yet, and after I've opened my eyes.
The process of starting to wake, fully waking up with my closed eyes, and opening eyes are all possible doorway moments for me--times of transition where things are more easily forgotten. These are times when I like to review in order to make sure I remember more and forget less.
Reviewing at all of these points improves my recall, but I am sometimes lazy and skip reviewing with closed eyes while awake if I'm feeling impatient. Doing all three is best for me, but doing two is still better than one. Doing even one of the review times during the waking process is also better than just doing it in lucid dreams.
Reviewing in lucid dreams also helps leave a memory trail of reviewing.
If I review my first dream in that dream and then my first and second dream in my second and my second and third dream in my third and etc, I can usually follow the trail back and forth pretty well even if I'm woken up suddenly as long as I remember a dream when I wake up.
My recall is a lot worse if I don't review in dreams or as I wake up.
If I hedge my bets on only doing reviewing during LDIW and then am woken up suddenly, my recall is much worse.
If I only do review in dream and not while waking, my recall is okay.
If I only do review during LDIW and not in my dreams throughout the night, my recall is okay.
If I do both, my recall is best.
It is work, and I can be lazy about it. Still, it has great results for me when I do it.
There are other benefits to reviewing. You can review a previous dream and use the review process to go back into that dream. This could be helpful for those establishing personal realms.
You can also better understand and memorize the feeling of dreams while reviewing them. Hukif claims it made him better at controlling GRC, for example. It’s a good opportunity to refresh yourself on things you did right in the dream that you wanted to get a better feel for—like scan, GRC, some dream control you liked, etc.
