Why use cumulative frequency?

Cumulative frequency gives the total number of events that occurred up to some value. Perhaps I want to show the number of accidents that occur in a year by the drivers age. A cumulative frequency plot would show me the total number of accidents from young drivers, say under the age of 21. I could easily come up with statistics such as 80% of all accidents occur from drivers ages 16 to 55, by examining the cumulative frequency.

Cumulative frequencies are used extensively in risk or reliability analysis. If I'm trying to find out how long light bulbs last, I may want statistics on the number that last less than 1,000 hours, or the lifetime as indicated by the manufacturer.

Another example: I may want to test the brakes of a car. I want to know the chances that the car will skid a long distance (further than the car is supposed to), so the cumulative frequency (long distances without stopping) is important.