Just a brief aside in a long series of posts about the subject (start here). I keep coming back to this subject. It has been discussed extensively, but it is of pivotal importance to RPGs IMO.
Let's imagine a gaming scenario where the group must search a series of woods looking for the MacGuffin - Woods A, B, and C. The MacGuffin could be in any of the woods. Pick a wood, pick any wood! It could be the classic Shell Game in D&D!
One DM - we'll call him Scripto-DM - scripts the content for all 3 woods in advance, and locks the MacGuffin into Wood B. The other DM - Improv-DM - makes a detailed encounter with an Ogre, and keeps that game content unassigned. Regardless of which woods the players choose first, he'd like the party to have the opportunity to encounter the ogre. The MacGuffin will be somewhere else.
Most folks will say that Scripto-DM has enabled player agency and free choice; Improv-DM is setting up a railroad. Let's first take a closer look at Improv-DM.
When the party boldly announces they will head out to Wood C first, looking for the MacGuffin, they run into Improv-DM's (supposedly excellent) Ogre encounter. He reasons that he could have improvised the woods with random encounter tables, but instead developed an encounter in advance. By deciding at game time that the MacGuffin is not in Wood C, and the Ogre is there instead, has he *actually* violated player agency? Player will or choice has not been thwarted. They wanted to go to the woods, and Lo! - they are in the woods. And yet objectively he has preordained a game result.
Now, think of random encounter tables. They are fun, IMO.
Roll 1d20. If you get a 17 the result is an... ogre.
If you have a single encounter table for Woods A, B, and C, and roll a 17, this is nearly the same as plotting an encounter in advance. The random ogre is almost a quantum ogre.
Think of it this way: it would be easier to "roll" for weather for say, one week, in advance. Same could be said for random encounters. Nothing wrong with rolling them beforehand. And if you get an ogre, the PCs get an ogre, no matter where they go (except, of course, if they decide to leave the woods).
Now the random ogre is undistinguishable from the quantum ogre.
Can you tell the two apart? I am not sure I can.
And I'm also not sure if this is always bad.
Planning "the party will meet an ogre tomorrow regardless of what they do" feels forced and rail-roady. But it is easy to see how the PCs didn't lose all agency - they can decide to hide, make a fire, go through a bridge, or into an abandoned cabin to rest for the day, and each choice will alter the conditions of the encounter.
It happened in one of my Curse of Strahd games (which has some encounters that happen "when you feel appropriate", which I disliked). For some reason I can't quite remember, a nearby skeleton would reanimate at midnight or something. I thought that would be a cool encounter. But the PCs decided to lock themselves into a tower.
So the skeleton came knocking.
They never opened the door. Nothing happened. They found the bones near the door the next morning.
It was a creepy, it was fun.
Maybe there is something to this.
No conclusions for this one. Maybe I'm a bit tired today. Just a few random thoughts, and I hope we can discuss some of these ideas in the comments.