I would like to add something else here to what Primo said. Oil begins to break down from the get-go, as he said. But, oil also begins to get dirty from the get-go. Actually, probably the most important reason for changing oil is that it's the only way to clean the crankcase. By-products of combustion deposit all kinds of nasty things in the crankcase including acids, moisture and other contaminants. Unless you have a little miniature man with a scrub brush that you can put to work in the crankcase, draining the old and pouring in new is the ONLY way you can clean the crankcase of all these nasty contaminants.
Lubricants have advanced drastically, and not only the great synthetics, but the dino oil as well. The base stock in the dino oil is much the same, but the additives, and the particular blends of all these great additives have taken a quantum leap in recent years. These improved blends do indeed allow you to run the oil a little longer than in years past. But, keep in mind that to keep the engine purged of all these corrosive contaminants, you must drain the oil. The more often you drain it, the less nasty contaminants are down there working 24 hours a day, trying to eat everything up.
I'm very glad to see that I'm not the only one here who believes that the idea of breaking in oil is "preposterous".
Have a great day,