If the wheels are parallel when the plane is in level attitude, then the wheels toe-out when the tail is down. This makes the plane very squirrely. Toe-in of the wheels in level position corrects this. On the Luscomb 8E I used to fly, the tail wheel had a lock that could be overcome when swinging the plane around with a brake applied. This lock did not seem to help as the plane was very squirrely on the ground. One got used to it, and learned to anticipate the wiggles and prevent them.