Carbon films are somewhat more resistant to deterioration in the presence of ionic contaminants and moisture. Otherwise, they tend to have higher voltage coefficients and resistance temperature coefficients. These may account for their specific "sound" in some circuits. Carbon composition R's can be quite rugged under pulsed overload.
Above a certain value it is hard to make metal films, but carbon films can be deposited on blanks to make R's about as big as you like, even exceeding 10^12 ohms.