How did the practice of using enslaved workers support the Southern economy?

It allowed for the South to have a cheap labor force to do their work. It boosted their profits because they could buy more enslaved workers for a cheap price.

People in the south used slaves because their economy was focussed on things like cash crops (tobacco, cotton, etc.) These crops required a lot of work so farmers and plantation owners could not do it by themselves. So by using enslave persons they could harvest more crops, sell more, make more money, and in return boost the southern economy.