Not a requirement for a fun game, agreed. (Not everyone shares my aversion to what I described upthread as "faffing around" - ie one person's faffing is another person's play).Or your could do this through actual play, instead of metagaming.
Doing this out-of-game is a preference, not a requirement.
But I think it is a requirement, or something like a requirement, for the sort of play that Nameless1 and I are talking about. Because if you don't do it through metagaming, than the GM has no easy way to start the game. Instead (it seems to me) s/he is stuck with providing hooks in the traditional way - either the railroad way, if it's one hook, or the sandbox way, if it's multiple hooks - and waiting to see which one the players take up.
A game like this could evolve into a situation-based game over time. And I have GMed a few games, both AD&D and Rolemaster, that did this - started as a bit of a sandbox, but after several sessions of play morphed into situation-based games as the players bit at hooks and started to embed their PCs in the gameworld.
It was these experiences, in the late 1980s and early 1990s, which really showed me that a game could be run without railroading but with a much tighter focus than a sandbox (or at least what I think of as a sandbox - eg Classic Traveller or exploration D&D). It was only much later - more than 10 years later - that I became a FoRE and got a better handle on what it was I was actually doing, and how I could use the mechanics of the game to help support it. Although there is one Dragon article that predates Ron Edwards prominence in RPGing circles but which did have a big influence on my approach to play - Paul Suttie's "For King and Country" in Dragon 101. The main aim of the article is to argue against the alignment system. But in the course of the argument he also describes how a situation-based campaign might be set up - his main objection to alignment is that it needlessly gets in the way of setting up the situation. What's missing from his description is an account of how you can embed the PCs in the situation from the get-go. This is what I've come to understand better as a FoRE.