Use of he kill switch is highly pushed and taught in the BRC in the states. In situations where a rider may pop a clutch, or lose throttle control the instructors drill into the students' heads when trying to start, slow or stop their bikes. I always use my kill switch to shut off my engine before kicking out my side stand, or dismount to use the center. At night this is usefull because engine power is off, but my lights are still on. Since I have a detatched garage without any power or lights I use my headlight for seeing when opening the garage and pushing my bike inside.
Back in March when I was rear-ended at a toll booth I was pinned against the side of the booth. Untangling myself I moved to righten the bike and pulled on the throttle when I grabbed the right grip causing my bike to lurch forward slightly. Instantly I hit the kill switch and righted the scoot. In the event of a slide -- if possible -- hit the kill switch to prevent power to the rear wheel. Depending on the speed it may not prevent a high end slide, but anything to slow the wheel will help.
-Wolf