Stable coins were originally created to do as their names say, to be stable regardless of how volatile the crypto market is at any point in time. Soon, traders took it as an advantage for retaining their portfolio worth in  fiat currencies like USD and reverting back when the price went lower. This is one instance where using stable coins has been profitable. Aside from that, stable coins will be stable coins. In my opinion, Facebook's Libra tokens will be good for the crypto community not because they're profitable (which they aren't) but because more businesses and organizations will get aboard and support for crypto will span across more businesses.