[racket] Code that double checks is good, bad, other?

The open-endedness of this led me to write a bit, then read a few things,
then produce unnecessarily long responses, and so on, so I deleted
everything to spare people. I'll go with saying thanks for the input.

But here's an interesting related link:

http://blog.codinghorror.com/gold-plating/

Related because more general than double checking is any sort of code
changes that have (should have) no effect (refactoring). My OCD nature is
the cause of this thread. Are there acceptable shortcuts anywhere?
According to Neil's second paragraph, yes.
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