Cold things tend to condensate water vapours when brought in warm rooms.

but by that point, the moment it's in the airport again, it's toast

The problem is getting airflow through the system. If there's no turnover of the air then the problem is minute.

If you turn it on then warm, moist air is drawn into the cold chassis, and that's when the problems happen. If you don't turn it on then the air that was always in it it still there, and the problem is minimised.

So if it's extremely cold, don't turn it on.

Depends I guess, most components are specced to around or just under zero, some military spec stuff is down to -40C, I don't think your laptop would like -200C.

I think the concern for me of having a cold machine taken of a plane into UK weather right now (24C and humid as hell) is the condensation that would build up if I started sucking damp warm humid air into a stone cold machine.

Things shrink when cold, oil thickens, bearings don't like to not be lubricated. So I'd worry about fans and spinning disk drives mostly. Certainly no harm in letting a laptop get close to room temp before starting.

Batteries are a lot less efficient. I don't know whether discharging/using them in that state has a persisting negative effect, these days

Thermally induced contraction and expansion can become an issue, particularly with marginal cases.

I wonder about the tolerance some discrete components may exhibit, e.g capacitors. For that matter, how much does that resistor vary over larger temperature spreads?

Anyway, I let my equipment warm up (or, when very warm, cool down, e.g. sitting in the trunk of the car in summer).