It used to be really bad for engines! Mainly because the condensation inside a warming up engine mixes with combustion blow-by and produces quite a nasty acidic vapour. It used to rot exhausts from the inside out pretty quickly back in the day. Rod and main bearings didn't much like it either.
It's not so bad these days with modern oils, better quality metals and better production tolerances.
A decent run evaporates off all the harmful contaminants from the oil, clears out PCV lines of mayo, burns off localized carbon build ups on the piston crowns and spark plugs, shifts all the moisture from the exhaust, evaporates moisture from the air filter, MAF & coils...... in short, you don't want water and rich warm up gases inside the engine, and you definitely don't want damp sensors either. It's why engines feel so much better after a long run. Everything gets up to optimum operating temperature.
It's also why frequent oil changes are important. All of that warm up crap quickly deteriorates the oil.
I never have and never will buy a low mileage shop run car. I'd take 200K motorway mile car over a 20K school run car any day of the week.