Let's say you don't lower the outer legs and just pull the pins and let the inner legs drop to the ground. You then raise the nose 4" to unhitch it from the truck. Now you hit the autolevel button and the nose wants to lower 8" to become level. Since you only have 4" available the rear jacks will have to compensate and may try to lift all 4 tires off the ground.
On the other hand, if you let too much out initially you could run into an issue going the other direction.
I always let some out (a few inches) on my previous trailer to allow some leeway in either direction.