Some upcoming musicians, producers, and DJs think that they can do their mix using some music mastering tips or recent audio mastering apps services. While these services are convenient and cheaper, online mixing and mastering services have their limitations.
When you want to go commercial, stay relevant and popular in the music industry, you definitely will need a professional mastering touch on your mix.
The kind of sound output that your tracks will need in order to be distributed in the music industry, sell well and be accepted by audio professionals is such that you can only get from a professional mastering engineer. Apart from getting a smooth, wrinkle free mix with unique characteristic pinned to your style of music from professional engineers, you stand to gain much more than what you pay.