For example, in this protocol for E. coli competent cell preparation, it says:
Plate 10 uL E. coli BL21(DE3) cells on a LB-agar plate; incubate overnight (12 hours).
Prepare 500 mL SOB medium so it can be pre-warmed in the 37 degrees Celsius incubator the day before.
Pick a single selected colony and inoculate in 5 mL of SOB medium and grow for 16 hours at 37 degrees Celsius and 250 rpm in a shaker.
Inoculate 500 mL of prewarmed SOB medium with 5 mL of the fresh overnight culture.
and then in the protocol for overexpressing proteins after transformation of these cells, I basically follow similar steps as above but this time, without prewarming the large-scale inoculation lqiuid medium. Why is that?