A further comment or two on "If you do it, you do it".
The departure from "Say 'yes' or roll the dice" means that the connection between (i)
stakes and
player intent for their PC in a scene, and (ii) the invocation of the resolution process, is less intimate than in a RPG that uses the "say 'yes' or roll the dice". There is no "saying yes": even if the player declares that they are seizing some trivial thing from a minor character by force, the dice have to be rolled and there is thus the possibility of a hard move from the GM (if the roll fails).
So instead of looking first to stakes/intent, we look first to types of behaviour - and
all seizings-by-force become laden with stakes.
@Campbell has often posted about this feature of the game, and was the first person I read who clearly articulated the contrast with "say 'yes' or roll the dice".
A second difference is from systems (such as 5e D&D) that require the GM to first determine whether there is a chance of failure, and then call for a roll based on that judgement. This imposes a certain responsibility for outcomes directly onto the GM. "If you do it, you do it" removes any such responsibility from the GM
in the context of the player-side-move-triggering actions. The player-side moves thus become one key component of the play-to-find-out apparatus. The other key component is the rule about when a GM can make a hard move in the absence of a 6- roll (namely, when a player hands a golden opportunity by proceeding in disregard of a prior soft move).
When I used to play a lot of RM, we rolled the dice every time that the rules called for it. But the difference from "if you do it, you do it" was that - at least in principle -
everything is a player-side move, and thus those moves do no work in channelling play in a particular thematic direction. And also, because rolling the dice in every moment of play is impractical, (i) it slows play down, and (ii) it pushes play a bit more towards the 5e D&D model of only rolling when there is a chance of failure, with the result shifting of responsibility for outcomes onto the GM.
As I think I posted upthread, I think the earliest RPG to use a type of "if you do it, you do it" approach in the context of rules deliberately designed to focus on the thematic sort of stuff is Classic Traveller (1977). I don't want to exaggerate this - the probabilities are not as elegant as Apocalypse World, and there is little sense of a soft/hard move escalation except in the subsystem for wearing vacc suits. But I do think that it is somewhere in the neighbourhood.