A situation would be if you were to have to put the answer into a fraction, or you were speaking the answer it would be easier to say "Three fourths" rather than "point seventy-five"
Measuring in cooking is a very valid explanation. Measuring flour per say, by 3/4 of a cup is much easier than measuring using the metric system such as: 0.75. We are more accustomed to using fractions rather than decimals in America.
