Improvisation: Understanding music theory to the degree that a player can improvise a melody that fits in a certain key is a tough skill to master. It is also a skill that is generally not part of normal music curriculum, but is needed when playing with others.
Virtual Hand: Many people on this planet are visual learners, even for things like music. Being able to watch someone or, in this case, a hologram, play or chord or a phrase before trying yourself can be a great boon.
Virtual Band: As mentioned above, having a virtual band to practice your improvisational skills give the user an open environment to learn and hone their skills—without the need to pay a group of people to help.