Musicians tend to categorise themselves as a “sheet music reader” or a “play-by-ear musician”. This is often related to whether the person has had formal music lessons or taught themselves, but there may also simply be a natural inclination towards one or the other.
In the world of classical music learning and sheet music reading, ear training is a natural addition to your studies. As you learn to read notes on the page and to play them on your instrument, ear training provides the bridge between the two worlds, allowing you to “pre-hear” the music you will play, and and to improvise your own music without the need to write it down first.
Outside that world though, it can be unclear whether ear training is relevant or useful.