It depends on tolerance. In electronics you allow for tolerance (+/- 5%). In carpentry you allow for tolerance (+/- 5mm). In cooking we allow for a huge tolerance (a pinch of salt! To Taste!) In delis, we allow for tolerance (ask for 100g of sliced ham, get more like 105g of sliced ham).
But when creating a small circle on a computer screen, we suddenly use a dozen decimal places where one or two (and sometimes no decimal place) would do.