If what you pass to PFD is not a literal block or text, but an expression that calculates a block or text...that expression will be evaluated. It might just be wasteful calculation that gets discarded, or maybe it has side effects. Maybe you want those side effects when debugging is enabled or perhaps not, but it's dicey.
If inline debug printing interest you, the development of invisibles and -- for dumping might be worth looking at. The idea is years old now and could use some updating, but completely vanishing expressions are still very versatile: