What happens if we use too many neurons?

If we make our network architecture too complicated, two things will happen:

• We're likely to develop a high variance model
• The model will train slower than a less complicated model

If we add many layers, our gradients will get smaller and smaller until the first few layers barely train, which is called the vanishing gradient problem. We're nowhere near that yet, but we will talk about it later.

In (almost) the words of rap legend Christopher Wallace, aka Notorious B.I.G., the more neurons we come across, the more problems we see. With that said, the variance can be managed with dropout, regularization, and early stopping, and advances in GPU computing make deeper networks possible.

If I had to pick between a network with too many neurons or too few, and I only got to try one experiment, I'd prefer to err on the side of slightly too many.