Building codes is what we mean, many people buy homes without knowledge of these details. Homes that suffer from electrical fires that could have been avoided are not honored by insurance companies if they find out the owner knew about the problem. Many people simply ignore these codes without knowing that they were put in place for the safety of who else the homeowner and add to that the neighbors and anybody else who could be inconvenienced or killed by such a reckless disregard for compliance.
Some of the work around the house is very much routine such as replacing alight bulb and adding one. But totally re-wiring a kitchen or bathroom as a result of a DIY renovation might need a qualified electrician to do the work. Yes, even if you have all the knowledge and experience in the world and do know what you are doing.