A repeating theme I've learned over the years of practicing is that learning new material is one of the most rewarding aspects to musicianship. This is especially true if it's something I'm learning by ear. One of the biggest challenges has been to sound out harmonically complex piano music. I'm guilty of always looking for a sheet music version of something but there are still several tunes or at least versions of tunes I love that have never been offered as sheet music. This is especially true on live arrangements by artists like Rick Wakeman and other improvisers.
I'm trying to make it a regular part of my practice to incorporate learning new material by ear, at least on piano and guitar. These skills only improve through repetition, and although it's very incremental and almost impossible to discern at times, I do notice a gradual improvement. I suppose this would be ostensibly for the ultimate goal of becoming a better and more rounded musician, but I've also always felt immediate satisfaction for even the smallest bits of a new song I'm learning. Learning a new song for me feels like tapping into the mystical, almost. It's the muggle equivalent of learning a new spell.