A few issues may impact you as the new homeowner. Your insurance company could deny the claim if there was a fire or a personal injury. Unpermitted modifications may affect the marketability when you become the seller. Annoying neighbors may call code compliance officials. "If" you get caught, simply remove the illegal alterations.
On the other hand, I inspect a plethora of new homes that are inspected by the city and find many (not a few) code violations.
Find a qualified home inspector in your zip code: www.creia.org