I love the spaced repetition. But sometimes you want to do some extra study. Have some spare time and there are no cards ready for review. It would be great to choose say the top 5,10,15 etc cards you have had most difficulty with (that will be coming up for review next) and be able to test them in your own free time.

So as not to interrupt the spaced repetition if you do get it right or wrong when you do this bonus testing it doesn't affect the SRS algorithm. That is based only upon when the cards are up for review and you do the SRS test. This is just a bonus so you can do some extra study