In a nutshell, if the bottom of the ball nut is not in contact with the bumper stop, the drag pins are not full engaged in the shelf bracket(0.5\" flight, 0.7\" on ground). The tracks and shoes themselves are not enough to keep the gear from splaying outward, which would be \"bad\".
Figure 3-12 in your trusty -1 shows how to use both methods to secure the MLG. Section 3 is quite detailed regarding LG malfunctions.