Licensed electricians are required to know the current electrical code. If you go to the expense of changing or adding electrical, you ought to do it to the current requirements. Also, the professional will purchase the correct material, in the correct amounts, creating the least waste possible which can save you money in the end. Also, city inspectors will charge additional fees every time you fail inspection and they have to come back. But most importantly, there is always a risk of electrocution and arc burns when doing electrical repairs and installation—not to mention that incorrect electrical work has a nasty reputation for starting fires and causing total structure losses.