Where Danger Lives (1950) is, for the most part, standard-issue film noir of the sub-genre that might be called "Being punished for bad stuff you wanted to do but didn't actually do." This includes films like Detour and Hitchcock's Strangers On A Train. This explains Mitchum playing an unaccustomed "good guy" role, because he wants to do bad. Well, he didn't really want to kill Claude Rains, but he wasn't all that sorry when he thought he had. Besides Mitchum, photographer Nick Musuraca is on hand to provide all his cool shadows and long angles.
What makes the film stand out is a couple of long take scenes in which the characters can play out the deception, desperation, guilt and despair that is overtaking them. Most remarkable is the second-to-the-last scene, which runs about 7 minutes--most of a reel of 35mm film--in which Mitchum and his co-star, newcomer Faith Domergue, castigate and torture each other as they try to figure out a way of the tightening noose. Mitchum's character is trying not to pass out, having experienced a concussion 24 hours earlier, and he stumbles about, even at one point disappearing from view as falls off a bed, but the scene goes on. It is not a showy long take shot, as in Touch of Evil or Rope. It is unlikely that the original audience even noticed it, but it is an interesting choice.
So what do long takes do for noir? Rope fairly well establishes the principle that long takes are destructive to certain types of suspense, especially that which relies on emphasis of objects, expressions and other types of detail. Yet long takes have a suspense of their own, as they take place in real time and have the capacity to stretch time, especially empty time to an unbearable degree. Some directors make the mistake of using long takes for expositional scenes near the beginning, possibly because no close-ups are needed or perhaps they are bored and would like to get through the scenes faster. But they make the shoot harder and make it very difficult to excise unnecessary material. (The idea is that if you have a lot of angles covering a scene, it is easier to shape it, cut it, even change the order of events. If you shoot it one shot, you have no protection: the scene you shot is the finished scene. Most experienced directors will at least shoot some inserts to cut away to in order to get themselves out of trouble if necessary.)
But if noir is about the dark night of the soul, then long takes can make that dark night longer and more agonizing. Moreover, it preserves a sense of space among the characters and their setting. It would be interesting to survey the entire body of noir to see if shot lengths vary in any consistent way--longer or shorter--from the rest of Hollywood in the Classical Era.
See, there's a PhD. thesis all ready to go for someone with a stop watch and too much time...