I have Snap utilities installed in the user preferences (Lite) edition. Only the Pencil works. I also have the default cube showing. I now want to delete the cube and the snap utilities is then removed from by preferences. Would some please explain why this happens
Blender's UI is capable of only showing the functionality that is relevant to your actual selected object but not every addon makes use of that capability.
Snap Utilities are probably mesh based and therefore are designed to only be relevant to mesh objects. If no mesh object is selected (like the camera or the light in the startup scene) they simply will be hidden until a relevant object is selected.