If you infer from an edge, you'll get a guideline...which is infinite in length, but which should not be visible through solid surfaces.
If you infer from a point, you'll get a short dotted line of whatever length you measured, terminating in a construction point. Again, not visible through solid surfaces. These processes are the same whether you're inferring from raw geometry or geometry inside a group/component.
If you get anything else, it's most likely a graphics card issue.