BBF Why would you use it?
Simply because it separates your focusing from your shutter. Instead of asking your index finger to deal with two different things one after the other, you give it one single task (pressing the shutter at the perfect moment) while your thumb will deal with focusing.
I’ve become a huge advocate for making the switch to (BBF) back button focus as a result of shooting equine events. I think it is one of the most beneficial changes I have made to how I now focus and take pictures and I personally think it makes a huge difference and improvement
This BBF technique takes some getting used to, mainly because you will be used to your focus being set to your shutter button when you pressed the shutter half way down, then the shutter being tripped when you fully pressed the button. By using the BBF button to focus and focus only, you will be free to use your shutter button as just that, a shutter to capture the action.
Check your camera manual to learn how to set this up on your camera and try it out, I am sure you will find it useful.