Molecular plasmid amplification - Liquid preculture vs. overnight culture?? - (Sep/17/2012 )

Some protocols suggest a 4-8 hour preculture to precede the standard 12-16 hour bacteria culture to reach OD0.6. Does anyone know the exact purpose of this preculture and how much does it help with increasing plasmid amplification?

Guarantees you that the culture is alive, avoids the major lag phase you get with inoculating a large volume with tiny amounts, and also gives the bugs some time to express the plasmid before selection starts.