Cakes, Onions, and Ogres have layers, are you sure your code needs them?

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Anybody write java code out there?
Anybody have a data access layer?
How about a business layer?
How about a service layer?

Why?

I've heard all manner of crazy answers like:
It makes my code more flexible.
I can dynamically swap out components for one layer or another.
I need to keep things isolated so that a problem in one layer don't impact the other.

Convince me, because I'm just not sold at this point. I went through a number of projects with this fad back in the 2001-2005 timeframe and none of the theoretical benefits never seemed to emerge...

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