The old, or English system (gallons, pints, feet, inches, yards) is that it was intended by use for ordinary working people who buy big things and divide them. A yard, with its 36 inches, can easily be divided into 2,3,4,6,9,12,or 18 parts.

You can't do that with 100.

Same applies to 640 acres (one square mile).

However, if you are a scientist or accountant, and you want to do sophosticated calculations, then the metric system works better.