Any reason to use Ball Ammo?

[Roblex]

I am getting conflicting advice from players. Some say that with close convergence ball ammo does more damage while others say ball ammo is a hangover from when the RAF did not have enough AP & Incendiary to use it in all belts otherwise they would not have used ball at all. I have to say my ignorant brain would say anything that ball can do, AP can do better.
Similarly they never would have bothered with observer rounds as incendiary gave visual feedback plus damage.