I read somewhere recently that there was a major error made by NASA as a result of someone using metric measurements as if they were English measurements. Can you imagine such an error being made by scientists at the level of NASA engineers? I certainly can't. Obviously their introductory chemistry instructors did not emphasize the importance of this critical skill and they were able to mask their ignorance in upper level classes. This resulted in a major problem with a NASA satellite up in space.
At the level of the earthlings, however, the individual errors result in nothing more than a lower grade on a test or lab report. Insignificant in itself, however, predictive of larger problems down the road.
Uncertainty is critical in chemistry. Measurements must be precise and accurate.