Comment by mooreds
It's the same tradeoff of turning an excel spreadsheet into a proper program.
If you do so, you gain:
* the rigor of the SDLC
* reusability by other developers
* more flexible deployment
But you lose the ability for a non-programmer to make significant changes. Every change needs to go through the programmer now.
That is fine if the code is worth it, but not every bit of code is.
It also implies that an engineer has better understanding of what is supposed to be done and can discover all the error modes.
In my experience, most of the time the problem is in the input and interpretation of the data. Not fixable by a unit test.