I've seen this principle come up a few times but I don't think I fully understand it. For example, assuming a passage in a story where a protagonist enters person X's house and a particular room is described in much detail. The described detail does not necessarily advance the story but instead does "character building" hinting at the personality of person X. There literally could be a loaded gun hanging on the wall…
The best stories frequently break the principle. There is a ton of worldbuilding done in even simple-reading stories like the Hobbit, that are largely irrelevant to the greater whole, but serve to give the reader a better perspective. Mindlessly following Chekhov's Gun, in my opinion, will always result in pulp fiction. Whether it's TV or novels, or movies. If you've stripped a story down to the bare basics, all you'…
My personal favorite is how in Once Upon a Time in Hollywood, the "gun" is a dog.