Robert, I regularly use both the Imperial (a.k.a. Fractional) System and the Metric System. I embrace both systems, but in my years of observing; I've noticed some things are slowly changing. English is slowly becoming the language of choice and metric is becoming the measurement system of choice. This is not just my opinion - it is a statistical fact. Some people adapt easier to this transition more readily. As to your first question: it is simply a matter of preference, some people will tell you they are 72" tall - while an identical twin may say he or she is six feet tall. Both are correct and neither is wrong - it is simply a matter of how they are presenting the information.
This same correlation also can apply to metric...450mm is no more wrong or right than saying 45cm - it is just preference. I do engineering and product development and although I am in the (slow) process of retiring - I still deal with people worldwide using both systems. With metric, I often see an avoidance of decimals - which would mean that most of the time someone will use a number without decimals. As an example, in my experience it has been rare to see a number expressed as 23.7cm; but rather this number would usually have been expressed as 237mm (same distance, no decimals).
Where the Metric System outshines the Imperial System is in conversion from one type of measure to another. There is no easy conversion of inches or feet to pounds or gallons - there simply is no common denominator! With Metric, a cubic centimeter = 1 gram (of water). 1,000 cubic centimeters = 1 liter. 1 liter of water weighs 1 kilogram. There simply is not a direct way to use an integer to convert feet to pounds to quarts.
People that are raised-up using the metric system often take it for granted that these conversions are easy and direct! Often when this subject comes-up I tell people, "I was born Metric!" I really get some strange looks, and then follow-up by saying, "10 fingers & 10 toes". Some of the others still do not immediately follow this line-of-thought until I ask if they have 12 fingers or 16 toes?
Admittedly, change is inconvenient for everyone. I will probably still always have to do quick math to provide metric answers to random questions - but in my business, if the customer wants metric - that is what they get - and I am good with that!
I hope this helps! Take care!
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