This is mainly a thought about people with high crit and haste.
As a shadow priest we are ranges dps. Standing at 25 yard or more away from boss. We can only have 3 app up at the time. They move so slowly. Is it possible to have a 4th swp crit before the first app hits the boss?
If that is the case. Standing in melee range would drasticly decrease the travel time of the app. Resulting in more apps if you crit more often.