Punishing Shot is employed to best effect in a damage dealing/spike capacity. Combine with preparations such as Read the Wind and activate immediately after a powerful opening attack such as Marauder's Shot to achieve a sizeable damage output in a short period of time. It may also serve as a potent stand-alone interrupt if needed.
After this skill has been used, there is a ¾ second aftercast delay before your next action may be undertaken.
If you wish merely to interrupt, consider Savage Shot, which is not Elite, though the bonus damage applies only if interrupting a spell. If an interrupt-intensive build is desired, both Savage and Punishing may be used in concert.