I have a very unorthodox approach to EQ because I have zero formal training so I have a lot to learn, but one of the most important things I do, for me, is putting a hard 4x eq high pass and low pass at the end of every chain on every instrument. This part might might sound dumb but I close my eyes and slowly close the filter until I hear a noticeable change in timbre. Often times I'll remove huge amounts of high and low end from sounds, much more than anticipated.
Timbre, in my opinion, is the most important aspect of a production. I will design a new sound to use with certain notes just to make sure the timbre is right. With EQ, I think abandoning certain "rules" is incredibly important to make sure timber stays in tact. For example, I will use volume modulation with volume shaper by cableguys or any other "brick-wall" style compressor to give instruments room to breathe at certain frequency ranges before I start cutting sacrificing frequencies. In the song in my profile the main bass pluck hits hard in the 100-200 range, and so does the sub that I layered it on, which interferes with my kick. If I cut those frequencies it loses its character, so I brickwall them for almost an eighth note to allow the kick to get its time in the limelight. The sub pluck hits at that frequency very early in the sound and dives by 12 semitones, where the mid bass doesn't hit that area until later in the envelope, so they don't particularly overlap.
I think this is a long winded way of saying that over EQing can turn songs into a brick that is a little too neat and loses its soul. I like to listen to songs that I think have good production (read: doesn't have to be a mord fustang or madeon or whoever tune), and throw them in ableton then listen to certain frequency bands using a filter to see whats going on. Most of the time you will hear all kinds of shit besides just the kick drum or sub bass hitting in the sub 100hz range, which makes you wonder why some people are so adamant about high passing everything.
I'm easily the most annoying poster on here. All my shit is long winded.
TL:DR version:
EQ is a matter of taste as long as your songs aren't muddy and don't clip.