Any law, including a speed limit, has unforeseen consequences. In my part of the world, there is a 4km stretch of the road with good visibility, low pedestrian

Any law, including a speed limit, has unforeseen consequences. In my part of the world, there is a 4km stretch of the road with good visibility, low pedestrian traffic, and which takes you either 10 minutes to go through if you follow the limits, or 3 minutes if you drive at +5km/h. Other than lost time (which compounds, but also increases traffic congestion, so those 10 mins might turn into 20-25), the fuel use and pollution are greatly increased. Interestingly, there are speed cameras there, and enforcement is not done on these slight violations: without this flexibility, I'd need to ask for traffic lights to be adjusted so they work well for driving under speed limits, and that is slow and an annoying process. But without an option to "try", I wouldn't even know this is the case, and I wouldn't even be able to offer this as a suggestion. Whether that accounts for consequences being "grave and terrible", probably not, but very suboptimal for sure.