Mastering music is a part of the music production that is concealed in mystery. Moreover, it is the final stage in the music production process. Unfortunately, a lot of musicians fail to recognize how integral proper mastering is.
These days, there are mastering plugins and online tools that claim to automatically master music. However, it is not comparable to the work of a professional mastering engineer. Mastering is more than just compressing tracks and adding EQ. Avoid using cheap or automatic computer generated services. Better yet, hire an experienced professional mastering engineer.
Read more about this here: https://sundownsessionsstudio.com/mastering-music-reasons/