I think there is something to the theory of dissociated mechanics even if I don't understand it. I think I don't understand it because I approach mechanics from a different perspective - more metagame, I think: a focus on the choices the players make instead of the choices of the PCs.
My first encounter with the theory went something like this (I think):
Me, reading the theory: 4E dissociates the choice the player makes from the choice the character makes.
Me: Is that a problem? The choice the player makes is the important thing. Since the character doesn't exist, you can decide what choice he made and why.
Me, reading the theory: But the 4E Daily/Encounter mechanics means that the PC can't make choices based on the game world.
Me: Is that a problem? The PC doesn't exist. You have to decide what the PC is actually thinking, so just make that something that works for you.
Me, reading the theory: But that means that the player can't interact with the game world. The player can't make choices based on what's happening in the fiction.
Me: Oh, okay. Yeah. I've been thinking about that a lot lately. Why didn't you say that in the first place?
Later on, after applying the lessons learned from dissociated mechanics to my own 4E hack - to the point of making it "not D&D" by my own standards:
Me: So if what's important is that the player can't interact with the game world - that is, make choices based on the in-game fictional details - how is that different from what's going on in older versions of D&D, with their abstract "to-hit" rolls, HP, turn-based initiative, saving throws, etc.?
(Playing 3E concurrently with my 4E Hack brings this point home. At one point we tried to resolve the
actual actions my PC took in a sword duel, as we do in my hack, and it made no sense at all. Erm, that's not true - it did make sense. It was just that the actions that seemed to me, at the time, to be the "logical" option flowing from the details of the game world were made obviously and supremely sub-optimal by the mechanics of the game system. Much better to ignore the game world and just say "I hit him with my longsword held in two hands, power attack for 5".)
Now maybe dissociated mechanics have nothing to do with the choices the players make. Maybe that's where my misunderstanding lies. At that point I respond, "Is that a problem? The game is about the choices the players make." If that's true: Obviously some people do care about something other than the choices the players make, but that viewpoint is very alien to me, and that's why I struggle to understand the theory.