Help different tracks fit together more cohesively in the mix (balance).
Remove unwanted noise (most typically “mud” in the low frequencies) from the mix.
Emphasize pleasing frequencies.
Help some tracks or parts of the song stand out more.
Create more separation between tracks (especially if, for example, you have multiple instruments occupying similar frequencies).
Deemphasize harsh or unwanted frequencies.
Of course there are a lot more things EQs can address! In the end, you simply need to be aware of what your goals are.
