Much has been made of 1917 being shot and edited to appear as though it is one unbroken shot. Sometimes where the cuts occur is pretty easy to guess - like moments of darkness.
There's an obvious cheat, too: at one point a character becomes unconscious during the daytime and awakens in darkness, taking away from the real-time feeling.
Regardless, 1917 is still an impressive technical achievement, covering a lot of ground (literally) and with many locations, extras, explosions and other challenges: a mistake at any point meant going back to the start of the take, so it's not like it's any easier to bring off than a conventionally shot and edited movie.
You could argue about the necessity of making it this way, of course. Does it provide immersion and immediacy, or come across as a self-conscious technical exercise rather than enhancing the drama?
Now the Oscar nominations have been announced, will 1917 be the second "fake one take" movie to win the best picture Oscar, after Birdman (2014)?
The "movie done in one shot" idea isn't new but it's only quite recently that technology has made it truly possible, whether truly a single shot or created via editing.
A notable example of a true one-shot movie is Russian Ark (2002), filmed in the Russian State Hermitage Museum.
An early attempt at simulating a single-shot film was Alfred Hitchcock's Rope (1948). It was shot in long takes with a prowling camera (and props being moved out of the way while filming) with not-so-invisible transitions using people's backs or objects filling the frame, and a few hard cuts at reel changes.
It's often regarded as an interesting experiment rather than one of Hitchcock's best movies, not making use of the more conventional editing that was a distinctive element of his filmmaking.
In the past, filmmakers had even more challenges to overcome than present-day filmmakers, for example in filming an amazing long take in I Am Cuba (1964).
It helps, too, if the technique is more than a gimmick: it can be used to increase suspense or tension, even it's only a particular shot, not a whole film. Orson Welles' Touch of Evil (1958) opens with a justly famous long take that starts with someone putting a time bomb in a car. The camera keeps track of the car as we wait for the explosion.
The other long take in the film is in an apartment and is much less flashy but even longer in duration and just as impressive in its claustrophobic way.
Apparently Welles, aware of the presence of a studio spy, rehearsed and shot the scene on the first day of production: this covered multiple script pages and put him days ahead of schedule.
Some "oners" are used to introduce characters and themes, like the wry self-referentiality of the opening single shot of The Player (1992). During the take, the film introduces characters as the camera moves around a studio lot, and one of them discusses the opening of Touch of Evil.
But sometimes they're not about movement but used simply for dramatic effect, like a woman gradually coming to the realisation a stranger is her long-lost daughter in Secrets and Lies (1996).
Done right, these long-take efforts are an impressive part of cinema.