Why is it not a good practice to unpack computer parts imediately after they have been delivered on a cold day?

Answer 1

Usually unpacking computer parts right away is frowned upon because cold items if heated rapidly tend to develop moisture (condensation) on them. This will be less prevelent if warmed to room temperature in a slower manner. The other reason could be that in conjunction with this moisture buildup, if you unpacked it right away and plugged the device in, the condensate could cause a short in the electronics.

Answer 2

In certain climates, during transit, the parts may have cooled to well below room temperature - most vans/trucks do not have heated load areas.

As you open the packaging, water vapour held in the relatively warm, moist air of the room may condense on the circuit board and components.

This water vapour, or "dew" may cause short-circuits and damage components on the card, or the even computer you are installing them into.