The metaphor is useful precisely because debt is not automatically bad. Taking a shortcut to validate an idea before investing in the proper implementation is often correct. What makes it damaging is taking it unknowingly, or taking it deliberately and never recording it.
The reliable symptom is that changes take longer than they should for reasons unrelated to their complexity — a small feature requiring edits in six places, or a fix that keeps reappearing. Teams that track debt explicitly, with the cost of the shortcut written down where it was taken, tend to pay it back before it compounds; teams that rely on remembering do not.
Codazz builds this in production — Legacy Modernization.