(Note: I didn't try the last update yet, so maybe things are properly implemented)

In the action of the race, it's sometime not obvious if you are the targeted one or if it's the opponent that just overtake you.

In such situation, avoiding to be just behind the opponent when hearing the red shell warning (it's often around one second) can save your life.

Without the red shell warning, you have no opportunity to react and you will simply get red shell that where definitely not for you (because there are no sound anymore if you are not the target).

Said otherwise : Taking a red shell without a warning now means the red shell was not for you. TBH, if the red shell was not for me, I would have preferred to have an opportunity to react and maybe avoid it.

Once again, such situation are not that common (but yet, not that uncommon) and it can bring some unnecessary frustration.