Memorisation is a valuable skill and being able to play through a piece from memory gives you freedom and confidence in performance. The printed score can be a crutch and can hamper expression. Memorisation can also be very useful for confronting nerves: with the score gone there is no safety net, you have to get the notes right. Proving to yourself that you can play the piece without the score is definitely confidence boosting. When you are memorising music try to play through the piece in your head away from your instrument. If you’ve really properly memorised a piece you should be able to sit down with a piece of manuscript paper (or a software program like Sibelius) and write it out. Don’t just rely on finger memory because this is what tends to fail when you are under the pressure of a performance. Know the notes as well as the fingerings.