Aside from also having an onboard sound card (which I delve into further down) every single function that your DJ controller does can be done just as, if not more, easily with a standard computer mouse.
There are many circumstances where running live sound in mono is just more practical. Especially when logistics dictate that one speaker will do the job just fine.
Most wedding ceremonies (not receptions) are run with only one speaker. And when it comes to lavalier mics worn by officiants, it can be challenging to also have the microphone pick up the newlyweds, as they pledge their vows.
This article is going to walk my fellow DJs through some ways that allow everybody to be heard, though one lavalier microphone, connected to one speaker.