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Pa systems

A lot of DJs have a PA system so they can be heard over a crowd to announce the next song or performer or get the crowd involved in their show.  The same effect can be had if you turn the music off and raise the volume on a microphone, but that’s for DJs who use microphones.  The DJs who are nothing more than human stereo systems that pick music and announce performers need PA systems every step of the way.  Your voice is not going to rise over a crowd of several people that are talking and carrying on at a louder volume than you could never dream of surpassing even if you screamed at the top of your lungs.
Most DJs aren’t going to use PA systems, but that doesn’t mean it’s an irrelevant part of the craft.  There’s a large subset of DJs that can’t go a day without using their PA system.  It works a lot of the time, but it also can lead to the DJ’s voice blending into the background.  You can’t get very loud with a PA system.  PA systems are used in schools to convey announcements to everyone in the school building.  These announcements often go ignored because the speaker’s voice is reduced to a dull murmur on a PA system.  The same goes for when a DJ decides to use one.
DJs need to be the life of the party.  They will have a hard time getting this done using a PA system.