Are you referring to atonal music using composition systems such as the Scheonerg method? In that case, even if most of it sounds dissonant, it's still composed

Are you referring to atonal music using composition systems such as the Scheonerg method? In that case, even if most of it sounds dissonant, it's still composed through a systematic approach, meaning notes/harmony are carefully choosen and left little room for 'out-of-box' improvisation