We would also rid a bull or extremely tough cow from the herd.
There is a difference between getting a cow hot and she gets on the fight, a wild cow that might need a little attention while handling and a flat out ignorant/mean cow or bull. The latter has to be culled. It is a danger to the horses and cowboys. These types usually have calves with the same temperament. Just like horses you don't want to breed undesireable characteristics into cattle, especially when holding heifers back.
Shooting them and eating on the ranch/station is a lot easier than hauling them to the auction. I imagine in AU it may be hundreds of miles to a sale. Eventually they all get their heads cut off anyhow, it is a matter of when. Hamburgers got to come from somewhere! :)
I DON'T LEAD 'EM AND FEED 'EM, I RIDE 'EM AND SLIDE 'EM.