Answer:
There are a lot of things that can go wrong, especially when we have an error in a measure that we use a lot of times (each time, that error increases).
For example, you think that each meter of fence costs $5, but the actual price is $5.30, and you need 40 meters, then you think that you may need to pay:
40*$5 = $200
But they will actually charge you:
40*$5.30 = $212.
Now this is a small example, now let's go to medicine, suppose that you want to trait cancer with radiation in a pacient, if you do not use precise measures for the dosage of radiation or the measures of the tumor, you may cause a lot of damage in the patient. (And similar cases if you want to give some medication and the numbers that you use are not precise, you may overdose the patient)
So the use of precise numbers may be critical in a lot of scenarios.
