The advantage of the finger roll is that the ball can travel high in the air over a defender that might otherwise block a regular jump shot or dunk, while the spin applied by the rolling over the fingers will carry the ball to the basket off the backboard.
[1] The finger roll is notorious for being very difficult to master, and few players use it as their primary shot.
One famous exception was San Antonio Spurs forward George Gervin, who turned the shot into a nearly unstoppable weapon when he led the National Basketball Association (NBA) in scoring between 1978 and 1980.
Although the finger roll is a very challenging shot, it still has a high percentage of making the basket.
Once there is opening down the lane for a layup, the finger roll is the most convenient due to distance away from the rim.