Guitar killwitches work by momentarily cutting the signal to your guitar pickups buckethead killswitch, iron age guitar accessories kill switchwhen pressed, essentially silencing your guitar, and resuming connection when the button is released.
The switch can be used rhythmically to create a stuttering/staccato effect. By doing this, you can produce a chopped percussive effect which can greatly contrast to a dampened palm mute.
Before killswitches, this same effect was commonly produced on guitars such as the Les Paul by having either neck or bridge pickup turned up and the other turned off. The guitarist could then flip the pickup selector back-and-forth at a rapid pace. While this is known to work just fine for some, it does require quite a bit of effort & may not be as agile as tapping a push-button.
Notable Guitarists: Some known players who incorporate the use of a killswitch are Eddie Van Halen, which he uses on his own Wolfgang guitar. Jonny Greenwood from Radiohead has also been known to use a killswitch on his signature telecaster. Tom Morello of Rage Against The Machine& Audioslave is widely known to use a killswitch extensively.
A great example can be heard on the solo of "Bulls on Parade" when the switch is used in conjunction with a wah pedal to create his very own distinctive sound!
Last but not least, and the most prominent user of a killswitch, is Buckethead. You can hear him create sound-scapes & special effects that are out of this world! Note-worthy tracks are "Soothsayer" & "Jordan" amongst many others.
Pops & Crackles
Sometimes while operating a killswitch, a guitarist might be able to hear an audible pop as the button is pressed & the signal is cut. This is generally unwanted noise and is actually quite common, but mostly with clean & undistorted signals.
What causes the cringing 'pop' is actually the clean signal being clipped instantly as shown below. With a distorted tone however, the signal is already clipping at various intervals and so depressing the killswitch does not have such a profound effect on the soundwave.
All in all, a killswitch is best operated with high gain distortion tones where any sort of popping is imperceivable.