Defensive switching allows the defenders to save their energy effectively against cutters who strike deep. By communicating a switch, the defense is more effective by running less.
In higher levels of play, switches are commonly used against vertical stacks and horizonal stacks. The key point of these switches is for the defender to understand that their man is burning him deep and calling out to his teammate who's already deep to switch off their own defender and take his.
Communication is key in switches. If the defender who's deep does not hear or understands when the "SWITCH!" or "SWITCH OFF" call has been made, the defender who calls it will be left in the dust and an easy point will be scored.
In this example, cutter 3 is going deep and is much faster than their defender.
defender 3 will scream out to defender 2, "SWITCH" or "SWITCH OFF" or "SWITCH DEEP" or call out, "HELP DEEP". Anything to get defender 2's attention to implement a switch. If done successfully, 2 will move off his guy and take defender three streaking deep.
In the mean time, defender 3 will now switch off and defend against cutter 2 who most likely will be making an in cut towards the handler.
This is effective when there is already one defender deep. If two cutters on blue go deep at the same time, then the switch won't be as effective and 3 will have to continue running and try to catch up to their man.