A simpler and more compelling reason in my experience is that relating tables is so much easier with synthetic keys. You can decide how large your synthetic keys are based on uniqueness requirements, natural keys have their own size and format that would then be copied to make relations. And if uniqueness depends on several values to be unique then dealing with compound foreign keys isn't fun or efficient. At this point, there would have to be a very compelling reason to want to use natural keys to offset this and I've rarely seen them. A case that may come up is for a miscellaneous table to use the synthetic key from another table with another natural value that uniquely identifies a row. I wouldn't choose this route if you ever think you want to relate anything to rows in this table, they should be leaves related only to the synthetic key being used.