That's why there's no final answer to "layer: yes or no?". It depends. And as a developer it's your job to guess which decision is more likely to save you time

That's why there's no final answer to "layer: yes or no?". It depends. And as a developer it's your job to guess which decision is more likely to save you time (= money) in the future. There's no way to know the right answer for sure because it depends on further (business) decisions that aren't made yet.