EQ (equalization) is an incredibly useful tool when mixing music. For the main reasons why, see my article (and video) What is Equalization, Usually Called EQ? You can do so many things with EQ, which is probably the most underutilized audio editing tool there is – at least in the mixing realm.
Here is a cool tip for enhancing the stereo imaging – making things sound even wider and larger in your mix – from The Disc Makers Blog: http://blog.discmakers.com/2016/04/complimentary-eq-home-studio-audio-mix/
And here is the video to accompany the above article: