No one wants to read an info dump. Fewer want to read a "maid and butler" conversation. Can we get away with either option without compromising the story? Maybe, if our hero picks up new plot points from the shadows.
The Eavesdrop - when a character (and the audience) receives information from other characters when no one knows their conversation is being overheard. This can typically lead to a paradigm shift in any given story or add suspense during the reveal of new details.
This is, after all, how Jim Hawkins (above) learned of Mr. Silver's pirate life! He overheard this reveal by hiding in the bottom of a barrel. How about them apples?
If you're a David Eddings fan, you'll know what I'm talking about. The man is a master of The Eavesdrop, since this trope occurs in several of his works. C.S. Lewis did this with two characters in The Horse and His Boy - even Brandon Sanderson's Vin listened in on Kelsier early on in Mistborn.
Perhaps you're trying to avert a galactic war and end up hearing all you need to know while hiding in the eaves.
"Best place to reveal secrets, EVER!"
The downside to this trope, however, is misinformation - missing part of the conversation that frustrates the plot, rather than help. It could make an ogre out of anyone!
"So much for eating rats together ..."
A trick can be played when characters know they're being listened to - leading to messing with one's head.
(Long scene, best part at 3:38)
Much ado can be learned when you eavesdrop, be it serious or silly. Perhaps this remains an effective trope since eavesdropping is such a common practice. So long as people have ears, they will assuredly listen in.
Have you applied The Eavesdrop in your writing? Did it turn the story around or reveal intriguing details?
I'm David, and did I just say that out loud?