It is most important to flash your brake light when:

Flashing your brake light is most crucial when you are about to slow down suddenly because it serves as a warning signal to drivers behind you. Sudden stops can catch other motorists off guard, leading to potential accidents. By activating your brake light, you provide advanced notice that you are reducing speed unexpectedly, allowing following drivers to react accordingly and maintain a safe distance. This early warning helps ensure safer riding conditions for everyone on the road.

Other situations, such as stopping at a red light or turning a corner, typically involve predictable and gradual movements where a standard brake light may suffice without the need for flashing. Riding in a group presents different dynamics, and while signaling is important, the primary purpose of flashing is to alert others of an abrupt change in your speed.