A datum may be of a certain size, such that it is not visible in all views of the model. You can change the 3D model extents to intersect the boundary of the model, so that the datum will be visible in more views.
In the following example, the grid is not visible in the 2 section views of the model, because its 3D model extents do not intersect either section view plane.
To maximize 3D model extents
The grid is resized to the boundary of the model.