This is all what wiki said about it
Frogger used two Z80 CPUs
Bosconian, Dig Dug, Xevious, and Super Xevious use three Z80 microprocessors running in parallel for the main CPU, graphics, and sound.
I didn't understand why they used 3 Z80's , because most arcade games just use 1 Z80 chip.
When you're using 2 or 3 , Z80 CPUS, what is the advantage? runs faster but what else?