Where playing an instrument means balancing the handling of tempo, rhythm and notes while mastering your human limitations, a tool like SuperCollider lets you just define these bits as reactive variables. The focus in SuperCollider is on audio synthesis and algorithmic composition, that's closer to dynamically stringing a guitar in unique rule-based ways - mastering that means bridging music- and signal-processing theories while balancing your processing resources. Random generators in audio synthesis are mostly used to bring in some human depth to it.