Most parts have differing tolerances (you have iron, aluminum, steel, etc all mixed together). The tolerances are generally set so when items are hot (swollen) they fit decently tight. When the parts are cold, they arent fitting together real well because they all have different coefficients of expansion.
Let alone that oil isnt in its prime until it reaches a certain temp threshold, etc.
I wont beat on a car at all until it's up to op. temps.