Been speaking about this today. I all ways use running in oil or mineral oil due to synthetics causing rings not to bed in , but then he said why do new cars come from factory with synthetic oil in ! I realised I had no clue so does anyone know?

 

Running in is done at the factory when the engine is built.
We'll that was my understanding anyway.

By the time you get the engine it's already run in and had its first oil change.