I see some people say that they want to keep the unique sound of each headphone/Iem. Which I totally agree, but that is also the exact reason I use EQ!
For example, I feel like X headphone is suitable for female vocals, I would use EQ to further improve the strength and reduce the flaws of the headphone, from being great for female vocals to being perfect for it.

It does takes lots of work, especially when there is so much songs and genres. But to me, the ideal scenario is that I know which Headphone/Iem to pair with the right EQ for each of my favourite songs. It sounds crazy. I know. I am so obsessed with it, that I have at least 3 EQs for each of headphone and IEM. It's fun tho, and the music is awesome. :D