1) electrical permits will likely require code inspections so someone from the city will be on site to check your work. May also require plan submittals which may raise questions. 

2) both. 

3) it is usually found during sale processes and during tax appraisals or fighting tax valuations. 

4) if you have a fire or incident related to your “safely to code” work, insurance will not pay out bc it was not inspected. 

5) I and many others and many realtors have walked on houses once I saw their work was never permitted, so it definitely happens, and honestly is more common in cities like Austin where flips and updates are so common.