First off, there's a whole school and practice of security measures which is aimed more at revealing breaches than in preventing them, per se. Audits, tamper-evident seals, tell-tales placed in maps, watermarks in documents or images, and very large swaths of system monitoring, reporting, and alerting. Much of military electronic security "Orange Book" procedures have much more to do with auditing than they do securing data.

Sometimes the goal is to determine what was taken or breached, sometimes who violated confidentiality (especially via watermarks or telltales), or how.

In some cases, the goal may be to ensure/assess planted information was actually accessed. One counterintelligence mission, Operation Mincemeat from WWII involved landing a dead body (a deceased criminal if memory serves) with bogus military plans, and a pretty elaborate back-story, to mislead German intelligence into thinking an Allied attack would occur in Greece rather than Sicily. Part of the assessment of the plan involved determining whether or not the Germans had in fact examined the documents, and forensics showed that the corners of the papers indicated that they had been secured in a manner consistent with being photographed.

https://en.wikipedia.org/wiki/Operation_Mincemeat

Another case might be, say, a journalist who wanted to be able to positively demonstrate that electronics were accessed without authorization by officials (whether in a border crossing or some other means). The glitter polish trick would make for a useful and highly embarrassing bit of evidence which could be shown to the public in the form of before-after photographs.

No, it doesn't prevent access (and the title is misleading), but it does identify access.