Even with rules, it does not matter. Many gamers will still pick the way that is more fun for them. And a lot of players think of encounters as fun.In 1e as written, equal xp were gained for defeating or avoiding* an encounter, meaning the choice on how to approach it was a) completely in the hands of the players/PCs and b) many more options were available as the reward system didn't incent one over another.
True.Further, if your options come down to fighting an encounter and possibly-maybe-probably dying or sneaking past the encounter and not dying, the wise choice seems pretty clear.
The basic principle is the same though. The vast majority of players want to have fun and be entertained.Thankfully, RPGs are not TV shows; and thus we don't need them to be all action all the time. We're not trying to attract viewers so as to sell ad space.
I don't really like this anti-pre planning stance.The difference is, if I've put the ogre on the left side of the fork in advance, I've also put ways for the PCs to find out there's an ogre there, or at least there are ogres in the area. If there's a choice the players have to make, that choice is meaningful. Otherwise, it's the illusion of choice.
Should a DM pre plan something like an encounter on the left roadway, the players get all bent out of shape if they can't "avoid it" somehow.
But the casual DM has nothing pre made. So there is nothing anywhere. But when the characters go down the left roadway the DM just improvs an encounter out of thin air. The players can never avoid it, as it did not exist before the characters went down the left roadway. They can't avoid what does not exist.
Of course, it does allow the pre planning DM to just say "oh, I just improved this encounter out of thin air" and then the players can't complain....