Code words exist so that people who hear them and aren't in the know are kept in the dark, and whether they're being used by spies or professionals they help keep secrets that might otherwise cause problems if exposed.
For instance, if you're sitting in a hospital waiting room and you hear a "code red" alert go out over the intercom you're likely to picture someone dying, but a "code blue" somehow sounds less jarring.
Medical professionals will likewise use the term "unremarkable" to indicate there are no abnormalities, a word which would make some patients feel a bit deflated if they read their medical report.
Folks might also freak out a bit if they read words like "Dyscopia", "Horrendoma" or "Status Dramaticus" in their medical reports, but these are merely code words used by medical staff to describe patients.
See 34 Code Words Professionals Use To Keep You In The Dark here (NSFW due to language)