so, steam locomotives in the US get a rap for being dirty and blowing lots of smoke when they didn't like, actually do taht generally.
if there was smoke billowing from the stack, the crew were dong a bad job firing and driving the locomotive, that smoke is all unburnt/wasted fuel and all, so in actual service they tried not to do it.
but steam heritage came early, and so did the era of photo charters. and photographers all felt that the billowing clouds of smoke were very pretty and very striking in photographs, so they would ask the crew to fire a little bit dirtier, draft a little bit less, put a bit too much coal in the firebox, to get that result for the pretty photo.
it's like how as a rocket launch photographer, i enjoy the (increasingly few) launches with solid boosters (Atlas, SLS, soon Vulcan) more than i do the ones without, it adds more visual drama when there's a huge smoke trail.