The AF function buttons and Focus Preset are on all of the big telephotos. Depending on the body, they can be set to perform various functions. When covering field sports with my 400/2.8 and 300/2.8 I have the AF function buttons set to switch between One-Shot and AI-Servo.
As for the focus preset button, I've tried to use it on several occasions but I don't find it very useful. Don't get me wrong, I can think up several scenarios where you COULD use it, I'm just saying that in actual field use it doesn't bring much to the table - for me anyway.
One example: You're shooting baseball, let's say from the first base side of the diamond. Runner on first. You set your pre-focus to second base, then go ahead and shoot the pitcher, or batter. Ground ball hit or runner trying to steal, you quickly swivel your lens to second base while activating the preset focus and fire when ready. This eliminates the need for having to acquire focus before shooting--it's already been acquired.
