I am sorry if you feel the words "engineering practice" takes this out of context for a "beginner". But I have found that one of the least understood rules for sizing an electrical system is proper sizing of the components. If you want a system that is reliable and fairly resilient, sizing the components for nominal power requirements is a recipe for failure.
As he stated he is a "beginner" looking to " Understanding Electronics Better" I wanted to let him know one of the most fundamental rules of sizing electrical systems components that all beginners should know.