Edit: This made me think about the scale of things you're measuring. Roads are generally best measured in miles, not yards, feet, or inches. Some things are better measured in yards (like football fields or concrete (cubic yards)). Some things are best measured in feet, and some things in inches.
The avoirdupois system is human sized. The metric system is based on some inaccurate 18th century French calculation of the circumference of the earth, IIRC. Why would you care what your height is in relationship to the circumference of the earth? That never made sense to me.
Rarely does it matter if you can convert from one unit to the other. The only exception I can think of is when doubling or halving a recipe - going from teaspoons to tablespoons or liquid ounces can be a pain.
Maybe I have to cover a road with 11 inch long bricks and I need to know how many to buy?
The problem is that although perhaps certain units may be good for measuring certain things, the things you use those measurements for will frequently involve things that use different units.
To take your road example again, what if I want to find out how many revolutions it takes a wheel with a 4 foot circumference to travel a mile? What if I want to find out how many yard long strides it takes to go down a road?
The metric units are interoperable. That's their big advantage.
Edit: This made me think about the scale of things you're measuring. Roads are generally best measured in miles, not yards, feet, or inches. Some things are better measured in yards (like football fields or concrete (cubic yards)). Some things are best measured in feet, and some things in inches.
The avoirdupois system is human sized. The metric system is based on some inaccurate 18th century French calculation of the circumference of the earth, IIRC. Why would you care what your height is in relationship to the circumference of the earth? That never made sense to me.
Rarely does it matter if you can convert from one unit to the other. The only exception I can think of is when doubling or halving a recipe - going from teaspoons to tablespoons or liquid ounces can be a pain.