That is, musical improvisation feels good and elates a person. You feel that you are at play. Your imagination is free to go wherever it wants and you are in a setting for spontaneous creation. The freedom that you are given makes you feel as though you are the hand of god. You are playing with this uncreated stuff like a sculptor working with clay, and you are working as the hand of god to create a beautiful articulation of the uncreated.
Restrictions teach discipline, which is absolutely necessary in improvisation.
The art of being able to let yourself go and surrender to the music while maintaining a discipline of seriousness is hard to master. It is the same with meditation. The discipline that it takes to be seriously attentive in mediation is the same for improvisation. The whole point behind improvisation, and the spiritual awareness that can be attained from it, is that improvisation is a reflection of life. When you wake up in the morning, you have no idea where the day will take you or what may happen to you that day.