Tennis players are allowed to challenge line calls when the hawk-eye technology is available on court. Upon a successful challenge, I've seen the point getting reversed in some occasions and replayed in the others. When is the challenging player awarded the point on a good challenge?
Generally speaking, when the point is determined to be an unavoidable loss for their opponent, the challenger should be given the point.
Examples of such a situation may include
a second serve is called in. The challenge shows it was out. The challenger wins the point for a second consecutive service fault by their opponent.
a shot is long but the point is called good in favour of the player who last hit the ball. The challenge shows it was out. The challenger wins the point for their opponent not returning the ball within the court.
a shot is good and subsequently played in a way that would lose the point, but the previous shot is called out. The challenge shows it was in. The chair umpire determines that the call of out was not a hindrance to either player. The challenger wins the point for their opponent losing the point.