First example would be when player gets Stun / Backstab / Impact / Parried effect.
Input buffer is opened with function OpenInputBuffer.
When effect ends, it closes input buffer and performs action based on stored key.
It means that even if owner is stunned, and he presses roll input during that, character will start rolling right after stun ends.
Another example is using input buffer within animations.
In image above input buffer is opened / closed through ANS_InputBuffer.
It opens at 35% of the animation and closes at 55%.
It means that if owner will press roll input while animation is within this notify (buffer opened), it will start rolling right after notify ends (buffer closed).