A loner can win 40% of the game for you.
A Loner should be attempted whenever a player feels that they don't require their partner's help to take at least three tricks.
Although there is proof that it is sometimes better to go alone with a strong hand when your score is 8 or 9 than it is to play with your partner, for the most part, the wiser move is to simply bring your partner with you and try for two points.