As more and more people are using headphones for phone calls, movies, music, etc, it is important to consider the dosage of volume we experience daily. Listening to music, or any other loud sound, is recommended only for a specific amount of time based on the overall volume. Given an amount of volume, there is a calculated safe listening level.
Rather than calculating these time-weighted averages on our own, Apple has created a feature to identify volumes that may damage our hearing. The feature includes visual warnings and automatic adjustments that reduce our listening levels. Check out this article to learn more about this great feature: https://www.cnbc.com/2020/01/21/how-to-see-if-iphone-music-volume-is-too-loud-hurting-your-ears.html