The overstudy feature allows you to review moves with MoveTrainer® before they are due for review. It does not earn you XP points but it gives overstudy points. Sometimes when reviewing a set of moves that do give you points, you might have an overstudy move or two, this just means you already knew those moves well.
This feature allows you to re-test yourself earlier if you want to. Particularly useful for those difficult moves, but each line to be reviewed must be selected individually.
If you get a move wrong while overstudying, it's spaced learning timer will be reset and you'll have to start that one from scratch, just like it would happen if you had it wrong during normal review.
If you get the move right while overstudying, nothing changes, the spaced period remains as it is since you did not earn experience points for this.
Remember, the overstudy feature does not give you points towards the main leaderboard or your progress for your next badge/rank. However, it will award you points towards the course leaderboards to give you a little something for your effort.
The bonus earned from overstudy towards course leaderboards is shown in a cumulative score in your detailed profile as "overstudy".