The goal of any printed circuit board project is to design it correctly from the start since modifications can prove costly and push back your timeline. A heavy copper PCB is no exception.
Certain printed circuit boards are designed to produce more amperage (or the strength of the electrical current) through the trace. But the higher the power requirement, the thicker the copper you need in order to transmit the signal through the board. That is why heavy copper PCBs are used in higher amperage designs.