The Zoom Slope option is a useful shortcut to automatically zoom to the extents of the external boundary of your model. This allows you to quickly view all of your model geometry, maximized within the view.
If you wish to zoom to all entities of your model, including slip center grids, etc., then use the Zoom All option rather than Zoom Slope.
Zoom Slope is available in:
The Zoom sub-menu of the View menu,
The Zoom toolbar