Invented more than 2000 years ago, threaded fasteners are still the most important detachable components used today in the design & assembly of machinery.  But even after centuries of improvements, threaded fasteners still fail.
Frequently, designers find that mechanical modificaitons will not solve fastener assembly failures.
In these cases, threadlocking adhesives can cost-effectively  eliminate unwanted lateral movements that cause both tension relaxation & self-loosening.