The iOS 15 release brings an added treat if you're a fan of immersive audio: a better soundstage for your tunes. As hinted at WWDC in June, iOS 15 and iPadOS 15 users now have dynamic head tracking for spatial audio in Apple Music. So long as you're using the AirPods Pro or AirPods Max, instruments and vocals will have a fixed-in-place virtual presence — turn your head and that guitar or vocal will pan accordingly.
Apple had promised Apple Music head tracking in the fall, but hadn't directly linked it to iOS 15 at the time. You don't need Apple's higher-end AirPods if you're content with 'regular' spatial audio, although you will need some form of AirPods or Beats earphones if you want automatic Dolby Atmos support.
Yes, it's a not-so-subtle sales pitch for higher-end AirPods. It's only useful for that subset of the Apple Music catalog with spatial audio support, for that matter. All the same, it could be appreciated if you want a more natural-sounding (or at least, less jarring) approach to 360-degree audio.