I agree that layering has real cost there as anything else does, but I still think layering is extreamly important to a clear design, as long as you do it with a good PLAN. Lots of troubles are caused by bad designs under the cover of good principles, not those good principles themselves.

From time to time, I see people copy and paste code from one module to another, and then slightly modify them. Layering is usually the best way to save people's life under this kind of situation. and make it more beautiful. Copy and paste makes programmer's life miserable, as now you might have to change whole bunch of code for a slight modification that you would be able to make at a single point if you layering properly.

With layering in mind, now you start to establish the sense of digging the similarity between modules that usuaully looks totally unrelated, and an entire new world is opened for you and the people work with you.

Well the copy and paste stuff is just one extream (and most simple) example, but the most miserable one. As now programmers are turned into production lines, instead of human being who want to spend more time thinking and dreaming.

I don't mean to seem to discourage having abstraction layers. I'm all for them, as long as they are buying you something in the particular instance at hand.