I see two possible scenarios here: if the over-torqued fastener is part of a static assembly, for instance valves cover, etc. it would be somehow "safe" since there wouldn't much "pull" force on the fastener. Of course, you are still in risk of damaging the threads, break the bolt, etc. Second scenario would be the fastener as part of a movable assembly or assemblies that need to hold strong forces, like shock abs, head bolts, steering elements, brake calipers to mention a few. What happens is that in these assemblies, over-torqueing is already adding more stress to the fastener keeping them more near to their break point, or failure point. Normally, fasteners absorb some stress and can stretch up or deform to certain points, before breaking. Any violent or lightly excessive force on these would effectively make the assembly fail, either by fastener break, ripped off threads or worse breaking part of the assembly, when in the contrary, if they are correctly torqued could absorb the stress.
I have seen head bolts rip off the threads in the aluminum block because it got so overtighten it weaken the threads so cylinder compression did its job.