On a foul, the official should have the "entire play".

On an OOB call, the official might only have part of the play -- that is the ball can come from one area and go out on another.

So -- why not ask for help all the time? Because 99% (SWAG) of the time seeing just part of the play is sufficient. So, make the call and then have the partner provide help.

Yes, there are other ways to do it. But, by tradition, this way has been decreed to be "best" for the game.

Help ???
 

This is always part of my pregame:

For out-of-bounds help, let's get it right. Come together for a change if needed. If I have no idea and I look to
you for help, just give a directional signal. No need to come to me. Just point. If I signal but I get it wrong,
then blow the whistle and come to me. Tell me what you saw and let me decide if I’m going to change it.