Printed circuit board (PCB) manufacturing is a black art among the DIY community. If you’re putting together a prototype circuit, the process is very well established: get an Arduino or your microcontroller of choice, pick out some components, get a breadboard and wires, and then string everything together. Easy, low cost, and accessible.
However, what if your project becomes more complex? You can extend breadboard or perf-board work to a point, but the likelihood of making an error grows exponentially with project complexity. Nobody wants to end up with a circuit that looks like this:
Image credit: Big Mess o’ Wires