Using this option you can prevent a step from drawing.
A good use for this feature is when you end a called out Submodel with a Buffer exchange. In other words: there is a floating part in the last step of a submodel which is in place when the Submodel is attachted to the main model. You would need to use a final step to retrieve the buffer you set. You can then exclude that last step since it is not necessary to show that step in the Callout.
In tis example the submodel with the brick and pin is called out. Since it is not nesscesary to show the second step you can right-click the assembly image of step 2 and choose Don't Show This Step from the pop-up menu. The result is the image on the right.
The command 0 !LPUB NOSTEP will be added to the code just befor the STEP command in the submodel.