Plus the steam versions can be edited compared to the original source. Certain scenes removed or music changed. Which can ruin it.
Or they're the version from one specific country/original release version which may have had a load removed to fit an arbitrary run time for that "type of film" or era, especially if it was before the big multiscreen cinemas (IIRC 90 minutes was considered "best" for a lot of films back when most cinemas had maybe 1 or 2 screens as it meant they could do a showing every 2 hours or less)
I've lost track of the number of times i've watched a film and thought "I don't remember this" or "i'm sure this is missing something" and on looking at IMDB found that there was a UK cut and a US cut, or a theatrical cut and a directors one, and normally the streaming services will have one of the US cuts which may or may not be the directors/longer version.
That's before any of the other "versions" where you had things like the "aircraft" cut or "TV" cuts, and it's extremely rare for any streaming service to actually state what cut they're using, although the default does tend to be the US theatrical, or the UK theatrical if there is a difference (as the UK one will have BBFC approval whilst the US one might not) here.
So it can be something as "small" as a couple of short scenes, or a cut to drop it from an R, to something like Life Force where there there is something like 20 minutes that makes an absolutely massive difference in the story (much of it at the start where they give some background for what's going on).
I can't remember the one that is normally quoted, where the theatrical cut was junk, but the directors cut which added something like 30 minutes is considered excellent, let alone the likes of Blade Runner, Aliens etc.
