When you turn 66/67 into a percentage, you get 98.51%. That number shows how close the fraction is to a whole one. It’s just a tiny bit less than 100%.
Because the value is so high, 66/67 is often used to describe situations where something is almost complete. For example, a test score of 66 out of 67 questions answered correctly would be reported as 98.51 %.
In everyday language, saying “about 99 %” is a quick way to convey the same idea, but the exact figure of 98.51% gives a more precise picture when precision matters.