DMs can learn from Hitchcock.
Director Alfred Hitchcock believed that every element of every shot should be deliberate; that the smallest thing that appeared on screen should have an intention and a purpose; that purpose being to further the plot, theme and tone of the film. He was not the first or only proponent of this theory, but his works provide many accessible examples of this principle being put to practice.
How many of us have known the DM who embellishes his world with cascades of maps, scores of named NPCs, and encyclopaedias of historical facts and dates? How many of us have been that DM? (I raise my hand.) This kind of thing is fun for lots of people. Worldbuilding is great, and letting players explore those worlds is exciting.
It's not necessarily good storytelling, though. If you have a world you want to show people, go and write a novel. Make a film. Worldbuilding is ultimately about the worldbuilder; it's you pitting your toy soldiers against your toy heroes. An overly detailed world is just as offensive as an overly-competent Mary-Sue.
Roleplaying is not about you, it is about the players. Each and every aspect of your world should be about the players. History is character development; maps are foreshadowing. If knowing the world's history does not substantively change the way your players behave, it is wasted history. If you have a map marked with "Here be dragons", the players had better be going there, and you'd better have some dragons ready.
Your encounters exist because they change things. If nothing is different after the players kill the goblins, then there was no point in having them kill the goblins. Either the defeat of the goblins has a lasting impact on the game world, or it costs the players something valuable, or it teaches the characters a lesson about who they are and what they believe. Random encounters are masturbation.
Keep on the Shadowfell features a set of caves that there is no reason to visit. The only incentive to go there is if Balgron the Fat escapes the battle at the Chieftain's Lair, which is a problem with Balgron being able to flee at all rather than an exciting subplot that screams out for spelunking.
The caves take up six pages of the module. The total space devoted to fleshing out NPCs is less than one page. When designing an adventure, it is important to have your priorities right.