The importance of memorising solo classical repetoire is a philosophy which has only been introduced to, and indeed impressed on me over the last couple of years since learning with my current teacher Wissam Boustany. And it is now not only something which I do as a matter of course but something I also truly believe in.
In my experience the act of learning a piece by truly committing it to memory yields far more rewarding results, than learning by just reading 'the notes'. Once a piece is memorised, the player is able to really get into the heart of the music. Reading music can be very restrictive as the player may be tempted to allow editorial markings to dictate the way in which they learn, play and perform music. As an audience member as well as performer I also believe that in recitals, music stands can act as a physical barrier. It can stop the performer from being able to communicate what they really want to say with the music.
By learning something 'by heart' we really do imprint music in our hearts. Therefore when we play from memory, all barriers are removed and, the music that ensues is what we want, rather than what we are told to play. I believe this is an important way of keeping music interesting and exciting as every musician's individuality will impact slighty differently.