I reckon the recommendation is to do with differing rates of thermal expansion between the various metals in the engine. Certainly the 6 cylinder DB4/5&6 Aston engines needed preheating if the ambient temperature was sufficiently low, as the alloy block would contract faster than the steel crankshaft and 'grip' the crank.
Of course, once the engine was sufficiently clapped out and the tollerances were loose enough, the problem would go away (or be substituted for an entirely different problem).