Lot's mate.
Also, lots of times, the dog will mark the hole the rabbits about to pop out of, and will aso indicate when a rabbit has been pinned, not too far down the hole. Many a time, ive been able to stretch in and pull one out.
And many many times, the dog has found warrens i didnt even know existed.
One other - a number of times, the dog has found a ferret that has popped out of a hole way a long an over grown ditch etc, which was thought to be part of another set, or not seen.
A dog gives you the confidence to take on difficult buries when working alone.
The ferret co