Same here. It wasn’t until about level 4 or so I realized it.
A great way to use it is if, say, you’re at work and you happen to have a few minutes to kill, you can boot up a review session (where you could have some 50+ reviews), and immediately click the Wrap-Up icon. Doing 10 items should take under 10min when starting off, so it’s a great way to nip away at those reviews that keep piling up throughout the day.
This is how I learned it. (If I am wrong, anyone please correct me.) When you start any new review session, WaniKani will queue up 10 cards. These are the cards that it will show you. When you complete a card, it is removed from this list, and another not-reviewed card will be added to the list. There will always be 10 cards in the review pile (until you run out of cards to review).
Example: If you answer nine cards correctly (pronunciation and meaning), but you make a mistake on your tenth card, which card do you see next?
If you are limited to 10 cards, your next review will be the exact same card you got wrong.
If you are not limited to 10 cards, your next review will be one you have not reviewed yet.
When you stop after ten cards, you may have some cards you started and did not finish (pronunciation or meaning, but not both). The next time you review in WaniKani, I think these cards you have to review both sides, even if you reviewed one side earlier.
I hope I didn’t make my explanation confusion. This is based on information I heard from someone, and my own experience.
This just saved my wanikani life. I had been waiting for so many days for that ONE kanji to come through again. My reviews queue is very high because of one bad weekend and I felt a bit like I was drowning. UGHUGUGH! I can’t believe I didn’t know. Oh well, time to burn through this $#!+! Many thanks!
If it makes you feel better, I’m Level 17 and I learned this on Level 16. I do 98% of my studying with Tsurukame app on IOS which has an easy to find “wrap up” option which is so handy when I don’t feel like doing a huge review session, and I thought it was a feature specific to Tsurukame and not part of the actual Wanikani website.