Canon says:
Mode 1, Enables quieter shooting than with [Disable]. Continuous shooting is also possible.
Mode 2, When the shutter button is pressed completely, only one shot will be taken. While you keep holding down the shutter button, the camera operation will be suspended. This enables quieter shooting, and operation will resume once you return the shutter button to the halfway position. Even if continuous shooting is set, only a single shot will be taken.
Disable, Be sure to set it to [Disable] if you use a TS-E lens for shifting or tilting the lens or if you use an extension tube. If [Mode 1] or [Mode 2] is set, the standard exposure may not be obtained, or an irregular exposure may result.
I’d add that you want to disable it when using a 3rd party flash. Shouldn’t make a difference for LED/fluorescent flickering. Silent LV basically means an electronic first curtain (EFC). On the lower end models which lack this setting, they use an EFC by default.