If you thrash engines from day one youll get the engine working better sooner, but the engine wont last as long. The thrashing will wear the piston rings really quickly as the mineral oil thats put in engines from new does not protect as well as the semi or fully synthetic stuff put in afterwards. The pistons will move freer quicker, creating more power quicker, but thats because youve worn the piston rings down a lot in the early days. As time goes on, youll find youre burning oil as it passes the rings and gets into the combustion chamber. Engine rebuild time please.
If you take a bit more care running an engine in, youll take a little longer to get the best power out of the motor but it will last longer. The piston rings will wear at a more steady rate. The mineral oil in from new will allow the engine to wear enough to bed in nicely if you take it gently, then after the oil change at the 1000miles check you should have a nicely worn in engine that will last for ages. You must also allow for other components (suspension etc) to bed in as theyre all new too.
Ill be taking it easy in the first 1000miles in my Cup when it arrives in a weeks time, as I have done with my last car and my current bike.