Sleep increase the performance to learning (especially motor skill). In fact, a 20% learning advantage for those who sleep from a study the author did.
It was the early-night sleep, rich in deep NREM, that won out in terms of providing superior memory retention saving relative to late-night, REM-rich sleep.
Review the things you want to learn before bed can increase the chance of retaining those information.
More specifically, it is the last two hours of NREM sleep that enhance the motor skills of the participants (p127).
Memory is a limited resource and forgetting is the price we pay for remembering. Fortetting is as important as remembering.
One a study, sleep selectively, boosted the retention of the things you want to retain and avoids the strengthening of those unwanting memories. (p121)
Perhaps the movie Eternal Sunshine of the Spotless Mind is not so fictional after all. Maybe there are ways that we can have unwanted memories deleted by a special brain scanning machine.