Headphones Highly Recommended
There is an argument over the best method for cueing song and mixing songs live. Some DJs prefer to leave half of their head open to hear the live sound so that the other half of their head can hear what is about to be played – but others actually prefer to do that completely isolated from any of the live sound. As far as the latter option, it is less common but also has some distinct advantages over the other. For one, the leveling of your music can be heard entirely in one closed system. There are no sound travel delays and you will also have a very precise understanding of how to two volumes seem to mix with each other.
Leaving one ear open may give you a sense that you are connected to the live sound and what the audience is actually hearing, but it comes at the cost of hearing fatigue and a possible mismatch from both sides of your brains. When it comes to listening for pure enjoyment, both listening from speakers and headphones are correct in any given situation. Certain ambient noises aren’t picked up well enough on speakers, while some three dimensional noises are better suited for speaker listening.