As someone has probably said before, Metric is more precise, but Imperial is easier to use when estimating. Also, I've found that Imperial measurements are used more in informal contexts i.e. telling your friends that you are 6' 3" but stating that you are 190cm when you are asked to fill out a physical.
As an Aussie, I rarely have trouble with either system as it isn't that hard to convert Metric units to the equivalent Imperial measurement, though I find Fahrenheit is more useful in applications for cooking.
But, I believe that the convenience of each system comes down to the user's familiarity of it, and that the existence of the either system isn't particularly detrimental to anyone.
As an Aussie, I rarely have trouble with either system as it isn't that hard to convert Metric units to the equivalent Imperial measurement, though I find Fahrenheit is more useful in applications for cooking.
But, I believe that the convenience of each system comes down to the user's familiarity of it, and that the existence of the either system isn't particularly detrimental to anyone.