Why are Perl source filters bad and when is it OK to use them?

Question

It is \"common knowledge\" that source filters are bad and should not be used in production code.

When answering a a similar, but more specific question I couldn\'t

Answer 1

The problem I see is the same problem you encounter with any C/C++ macro more complex than defining a constant: It degrades your ability to understand what the code is doing by looking at it, because you're not looking at the code that actually executes.