Well, it's the concepts of "specialization" and "localization". You create an expert in the field of cookie jars and have that expert be the only person who knows how to handle cookie jars. That way, you can pretty much guarantee that no-one's going to screw up the cookie jar because they didn't know the correct way to get a cookie out while three other people are trying to do so as well.

As for slowing things down ... which do you prefer - "slow and correct" or "fast and wrong"? Except, "fast and wrong" is usually "runs fast, is wrong, and took way too long to write", while "slow and correct" is more often than not "runs fast enough, is provably correct, and came in ahead of schedule". I know which one I prefer ...