I once watched the 1941 version of The Maltese Falcon in San Francisco, and the audience started laughing when these words appeared on the screen.
Surely superfluous, they must have thought: who wouldn’t recognize San Francisco with all that stock footage of the city’s essentials? But San Francisco was a much smaller, less culturally significant city back then and many American movie goers would not even have heard of it much less been able to recognize it by sight.
I enjoy these “unnecessary explanations” in old films as historical curios. Another of my favorites is in the 1948 criminal investigation classic Call Northside 777. A suspect takes a lie detector test and a scientist explains what the machine does at what to modern audiences seems like inordinate length (after all, even in films like Deceiver that revolve entirely around a lie detector, there is no such lengthy exposition). The scientist is Leonarde Keeler, the co-inventor of the lie detector, a machine that audiences would not have heard of in 1948 and probably wouldn’t have taken as a credible plot point without all the sciency lecturing.
Similarly, another great police procedural of the same period, He Walked by Night, includes a detailed explanation of what a police composite sketch artist does because of course audiences at the time wouldn’t have already watched a million episodes of Law and Order on television.
Another notable example are “nature documentary moments” that appear in many films prior to the era of widespread television ownership, for example 1950’s King Solomon’s Mines. The characters in such films have plot-irrelevant conversations of the form:
Hero or Heroine: “What on earth is that?”
Grizzled Guide Who Knows the Local Terrain: “That is a leopard”
Hero or Heroine: Wow!
Pretty boring if you’ve seen a Jacques Cousteau special or virtually any hour of what plays on the Nature channel all day long. But audiences back then couldn’t watch television nature documentaries and few of them had access to exotic zoos or international travel either, so as dull as these bits of cinema are to us today, they amazed viewers at the time, and they teach discerning viewers about the period in which the movie was made.