I found an analogy with electronic circuits useful. You can implement any bitwise function using a single layer, a lookup table. The problem with that is it req

I found an analogy with electronic circuits useful. You can implement any bitwise function using a single layer, a lookup table. The problem with that is it requires as many logic gates as there are inputs, exponentially many. As a result, it's more efficient to design deeper circuits that compose multiple logic gates. The tradeoff is that it is slower to evaluate, since the signal has to pass through more logic gates.