The engineering community commonly uses the metric system, both because a lot of the early math and science was performed by Europeans, but also because it makes a bunch of calculations simpler.  English units have pounds of mass and pounds of force, which are both equivalent and not equivalent, depending on some criteria I have to look up every time I use them.  So it's common to scoff at people who use English units because it adds unnecessary complexity. 

But not all engineers use metric units.  Mechanical designers and metal machinists use English units, [I've heard] because the cutting tools use English units.  We don't have 6.4-mm screw holes; we have 1/4" screw holes because we have 1/4" drill bits.  Some raw materials come in thicknesses measured to the nearest 1/8" or 1/4". 

But at the same time, metal machining often specifies tolerances using a sort of semi-metric system, e.g. something is measured at 1/8" +/- 0.010" (spoken "ten thousandths").  Similarly some engineers use feet as a unit of distance, but if the magnitude of the values they deal with is greater than 10,000, they use the term "kilofeet", which is both beautiful and ugly at the same time. 

Electrical power is measured in Watts, but mechanical power is measured in horsepower.  [Hint:  they're the same thing, i.e. units of power.]  But it feels wrong to say I have a 147 kW engine in my car, or a 1.36 hp microwave in my kitchen.  It all comes down to what you're used to. 

The metric system is really just a standardized unit (m for length, kg for mass, etc.) plus a Latin or Greek prefix denoting the decimal point.  English units almost sort of use a crappy version of this with things like inches (10^0), feet (inches x 10^1.0792), yards (inches x 10^1.5563), miles (inches x 10^4.8018).  I don't know what the solution is, so I'm gonna go walk a few hundred mega-inches to de-stress. #science