Everyone has had great things to say about all the reasons to use a whip for cueing turns, bend etc.
I’d like to point out that carrying a whip is also about safety.
There may come a time while driving when something happens that puts you, your horse or someone else in immediate danger. You may need to make that horse move RIGHT NOW in a certain direction without thought to anything else. Using the whip as an immediate forward aid is a great way to do that.
If you have no whip, the consequences may be tragic.
Why take the chance of not carrying a whip?
NJR