Narrow gauge,  regardless of the gauge was done - in most part - for two reasons.   It was cheaper to do and the narrow gauge railroads usually ran where the standard gauge could not due to tightness of curves needed and grades.  For the most part, narrow gauge railroads were in place to handle mining or lumbering operations,  although, in New England,  some of the most narrow of the gauges, 24 inches, were used in the cranberry industry.