I know a guy who if you ask the temperature will give it to you in Celsius which is great except if you live in a place where its all given in Fahrenheit. He's the same guy who ended up being given a problem at work with mixed metric and standard that needed to be converted into the same units. On the other hand, my mother operates only in miles per hour and when we drove from Alaska to Washington State via Canada, I had to translate km into miles. Otherwise she would interpret the speed limit as being miles per hour rather than kilometers per hour. One good reason to be able to convert from metric to standard and back again but what are other reasons for knowing conversions.
We all know its used in science class which means students are good at converting in science but the minute they pass through the door, they forget what they learned especially if it requires you to do it in real life.
One example is if you want to redo the carpet in your house, most rooms are measured using feet and inches, yet carpeting is sold by the square yard. This is a type of conversion that they are likely to run into in real life. What about ceiling tiles, paint, or even flooring. These all require a type of conversions.
Certain jobs such as Pharmacy Technician need to be able to convert within the metric due to the medication prescriptions they fill. Nurses and other medical personnel need to know that 1 CC is the same as 1 milliliter of fluid. I once taught a basic math class for nurses at a small community college. That was one measurement we made sure they knew because it is used in work.
If you participate in local races, many are in kilometers rather than miles and its nice to know how far you will be running if you participate in a 10 km race. Its about 6.21 miles since 1 km = .621 of a mile. What about if you buy a free cookbook from Amazon and it turns out the author provides measurements in metric, you have to convert so you can make the dish. I have a few of those cookbooks myself.
Even if we don't want to know about conversions, we do need to know how to do them although most kids I know would tell me to go online and use a conversion calculator......LOL. I'd like to know your thoughts on why its important to know how to convert measurements.