There is an advantage in knowing the sound of certain freqs without consulting a spectrum analyzer.
For example being able to tell the difference between 200Hz and 250Hz without looking, only listening... it develops the ear to a much higher degree than taking the easy way out... finding a problem freq on an analyzer and then reaching for the EQ knob...
It's a crutch, much like the musician who never quite learns a song, because he keeps the music-stand close by.
It's a much greater discipline to hear a mix, imagine (in the mind's ear) what EQ corrections need to be made, execute them and then, see if you were right.
After awhile, you won't even need the analyzer, except for certain problems.
Admittedly, I keep one running in the studio, off to one side, but catch myself, if I stare at it too much.
Separates the men from the boys, so to speak.