I can't imagine running one where everything is predefined. Not only does that seem far too exhaustive, but it seems like you would have a very static sandbox as well.
I do appreciate the idea of 'pinning things down' during play. For example I may not know where all the teahouses are in a region because I didn't flesh that out. But if the players start talking about contacting them all: I will try to create some details on the spot and write them down in my notes so I have a bunch of relevant information (who operates what tea houses, what types of illegal activity might be going on here, if any are under the auspices of a protection racket or have imperial ties, location, what they are known for, etc). You can't think of everything in advance. Some of the setting details you will need to flesh out as the players explore. And I do like pinning down these details so there is a sense that they are exploring an objective place rather than one that bends and warps around them.