Active listening helps you develop the skill of audiation
, meaning imagining music in your mind.
When you practice active listening you're teaching your brain to conjure up vivid mental representations of music, and that's something you can then apply to music you're creating in your mind yourself as well as the music you've heard.
Audiation is a core skill that acts as the bedrock for much of what we do as musicians, whether we realise it or not. Improving your ability to audiate will help you learn, memorise, improvise and compose music, as well as playing it by ear.
For example with improvisation, to be truly free and creative you want to be imagining the music before you play it rather than just playing notes and hoping they sound good. Audiation is what lets you do that.
Audiation can also be used to more easily learn and memorise music, with what’s called “mental play” where you imagine yourself playing the music while it plays in your mind’s ear. This lets you actually improve your instrument skills even when you’re not physically playing.